Comparison

Calendars vs Opus One

Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.

Head to head
About

Calendars

This app combines a calendar, task manager, daily planner, and habit tracker. It helps users plan their day, build habits, boost productivity, and stay organized with seamless syncing across all Apple devices. Features include event creation, to-do list management, natural language input, and integration with popular meeting platforms.

Highlights
  • Calendar, task, and habit management
  • Daily, weekly, and monthly views
  • Natural language event creation
  • To-do list organization
  • Cross-device syncing
  • Meeting platform integration
Features
Read full description

Calendars by Readdle is the all-in-one calendar, task manager, daily planner, and habit tracker — seamlessly working across all your Apple devices: Mac, iPhone, iPad, and Apple Watch. Plan your day, build better habits, boost productivity, and stay organized with powerful features and smooth sync between all your devices. What you can do with Calendars: • View and manage your calendar with daily, weekly, and monthly views • Create events, set reminders, and never miss important dates • Use the built-in agenda planner to focus on what matters most • Organize your to-do list and manage your tasks with ease • Quickly add events or to-do items using natural language • Build routines and track your habits to stay consistent • Take a guided productivity course to improve time management and focus • Sync across devices with Google Calendar, iCloud, and more • Customize your planner calendar with color coding and widgets • Join Zoom, Google Meet, or GoToMeeting directly from your calendar • Stay in control of your time, wherever you are Whether you're planning a busy workday, building new habits, or working on personal growth, Calendars brings everything together to help you own your time — across all your Apple devices. Privacy Policy: https://readdle.com/calendars/legal/privacy Terms of Service: https://readdle.com/calendars/legal/terms Have questions, comments, or issues? Don’t hesitate to reach out to us at http://readdle.com/contact

About

Opus One

This app helps you manage tasks and notes with a paperlike interface. Organize your day with daily task lists, schedules, and notes, and use a master task section to capture all your to-dos. Features include drag-and-drop reordering, event integration, and customizable notes.

Highlights
  • Master Task section
  • Daily Task lists with status, priority, and notes
  • Daily Schedule and Event integration
  • Daily Notes with customizable text formatting
  • Drag and drop task reordering
  • Cloud synchronization
  • Sketch drawing canvas
Features
Read full description

Opus One is a real day planner, not another to-do app. Each day gets its own page — tasks with A/B/C priorities, your schedule, and notes — on a planner that looks and feels like paper. Plan on iPhone, iPad, and Mac, and it all stays in sync. YOUR DAY ON ONE PAGE • Daily Tasks with A/B/C priorities, status, notes, and alarms. • A schedule that shows your Calendar events alongside your tasks. • Drag a task onto the schedule — with task durations, the end time fills in automatically. • Daily Notes with photos, PDFs, checklists, and audio. • Today's weather and a daily quote, right on the page. PLAN BEYOND TODAY • Master Tasks: everything on your mind in one list, no due date required. • Goals with timelines, photos, and progress you can see. • Roles: review the areas of your life each week so nothing important gets crowded out. • Mission, Values, and Vision pages to keep the big picture one tap away. • Meeting Planner for agendas, decisions, and next steps. NOTES AND JOURNALS • Rich notes with fonts, colors, tags, and your own custom sections. • Sketch and handwrite with Apple Pencil. • Journals with 25 covers to choose from, plus a guided Gratitude Journal. IT GOES WHERE YOU GO • Home Screen widgets for today's tasks, your mission, your values, and daily quotes. • Live Activities keep today's tasks on your Lock Screen. • Add a task from Control Center, or ask Siri. • Apple Watch app to see your day and check off tasks from your wrist. • iCloud sync across iPhone, iPad, and Mac. MAKE IT YOURS • Planner themes, including seasonal ones. • Task-complete sounds and rewards for finishing what you planned. • Color-coded categories and repeating rules with advanced options. OPUS ONE PRO The core planner is free. Opus One Pro adds cloud sync across all your devices, weather, attachments (images, PDFs, audio), Apple Pencil sketching, categories, repeating rules, Goals, Siri, and themes. One subscription covers iPhone, iPad, and Mac on the same iCloud account. Available yearly or monthly. Subscription details: Payment is charged to your Apple Account at confirmation of purchase. The subscription renews automatically unless auto-renew is turned off at least 24 hours before the end of the current period, and your account is charged for renewal within 24 hours before the period ends. Manage or cancel in your Account Settings. Privacy Policy: https://piso13.com/privacy-policy-2/ Terms of Service: https://piso13.com/terms-of-service/

Screenshots

Calendars4 screens
Opus One4 screens

Verdict

The call

The clearest difference is monetization model: Calendars at free with in-app purchases against Opus One's subscription. Calendars also leads on ratings volume (122K vs 978) and update cadence (weekly vs every 3 weeks). Opus One's advantage is review sentiment (66% vs 56%) and iOS requirement (15.0 vs 18.2). On price, rating, ads and in-app purchases there is nothing between them.

Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS

CostPrice · In-app purchases · Ads · Monetization

Both are free to download. Calendars sells 18 in-app purchases, starting at $3.99 per month and Opus One sells 2 in-app purchases, starting at $4.99 per month. Whichever you choose, the download price is not the number that matters.

ReceptionRating · Positive reviews · Number of ratings

On the App Store both sit at effectively the same score — 4.7 for Calendars against 4.7 for Opus One. That said, the two scores are not equally well evidenced: Calendars has 122K ratings behind it against 978, so its average is the more settled of the two. Written reviews are what separate them: 56% of Calendars's written reviews are positive against 66% of Opus One's.

UpkeepUpdate frequency

Calendars ships an update weekly, Opus One every 3 weeks. The most recent releases landed on October 28, 2026 and October 26, 2026 respectively.

Scorecard6 real differences · 5 level
Calendars versus Opus One: the parameters behind the verdict, then further details
ParameterCalendarsOpus One
PriceFreeFree
Rating4.7 (122K ratings) — better4.7 (978 ratings)
Positive reviews55.8% of reviews65.7% of reviews — better
Number of ratings122K — better978
Update frequencyWeekly — betterEvery 3 weeks
AdsNoNo
In-app purchasesYesYes
MonetizationFree with in-app purchases — betterSubscription
Best chart rank#117 — better—
DevicesiPhone, iPad, Mac, Apple WatchiPhone, iPad, iPod, Apple Watch
Requires iOS18.215.0 — better
Further details — not scored
Size412 MB187 MB
Age rating4+4+
DeveloperReaddle Technologies LimitedPISO 13, Inc.

Customer experience

Calendars

All ratings122,379 ratings
Positive93.8%
Neutral3.1%
Negative3.1%
Written reviews1,286 reviews
Positive55.8%
Neutral8.6%
Negative35.6%

Opus One

All ratings973 ratings
Positive93.6%
Neutral2.5%
Negative3.9%
Written reviews318 reviews
Positive65.7%
Neutral10.1%
Negative24.2%

User reviews

Calendars

From 122K App Store ratings

What we love

  • 🌟 Excellent calendar app
  • 👍 Easy to use and organize
  • 🎨 Helpful color-coding
  • 📆 Seamless integration with other calendars
  • 🗓️ Detailed monthly/weekly views

Room to improve

  • 🐛 Occasional glitches and data loss
  • 💰 Concerns over subscription model
  • 🕰️ Cumbersome date/time selection process
  • 🔍 Limited location search functionality
  • 🔄 Sync issues between devices

Opus One

From 978 App Store ratings

What we love

  • 🚀 Life changing
  • 👍 Great app and support
  • 👍 Integrates well with iPhone
  • 👍 Keeps me organized and efficient
  • 👍 Seamless sync across devices

Room to improve

  • 🐛 Sync issues and reliability problems
  • 🐛 Lost data and app crashes
  • 🔒 Concerns about free trial sign-ups
  • 🔒 Difficult to cancel subscription
  • 👎 Lacks weekly/monthly views

Bugs and requests

Calendars

Reported bugs

3 issues
  • Disappearing events and appointments
  • Upgrade process causing data loss
  • Freezing and crashing on certain devices

Requested features

5 requests
  • Recurring events for free users
  • Customizable widgets and app icons
  • Ability to archive/restore past events
  • Improved Apple Watch integration
  • Shared calendars and family management

Opus One

Reported bugs

4 issues
  • Sync issues between devices
  • App crashes and data loss
  • Keyboard not working on iPad
  • Distorted font in calendar view

Requested features

6 requests
  • Add weekly and monthly views
  • Improve Apple Pencil support
  • Add project management features
  • Integrate with more calendar/task apps
  • Provide better training and tutorials
Show 1 more
  • Allow customization of UI and themes

In-app purchases

18 purchases

Calendars

Subscriptions9
  • Calendars PRO 1 Month$3.991 Month
  • Calendars by Readdle: Interesting Calendars1 Month trial$3.991 Year
  • Calendars PRO 1 Month7 Days trial$3.991 Month
Show 6 more
  • Calendars PRO 1 Year3 Months trial$19.991 Year
  • Calendars PRO 1 Year7 Days trial2 variants$19.991 Year
  • Calendars PRO 1 Year1 Year trial$19.991 Year
  • Calendars PRO 1 Year14 Days trial$19.991 Year
  • Calendars PRO 1 Year7 Days trial$21.991 Year
  • Calendars PRO 1 Year7 Days trial$29.991 Year
One-time9
  • Calendars PRO LifetimeFree
  • Invites & Attendees Upgrade$1.99
  • Smart Input Upgrade$1.99
Show 6 more
  • Full Upgrade$4.99
  • Interesting Calendars$5.99
  • My schedule planner, Organizer$6.99
  • Full Pack$12.99
  • Reminders & Calendars$19.99
  • Recurring Events$31.99
2 purchases

Opus One

Subscriptions2
  • Opus One Pro7 Days trial$4.991 Month
  • Opus One Professional7 Days trial$39.991 Year

Questions

Is Calendars free?
Calendars is free to download, with in-app purchases available.
Is Opus One free?
Opus One is free to download, with in-app purchases available.
Which has better reviews, Calendars or Opus One?
Calendars is rated higher. Calendars averages 4.7 out of 5 from 122K ratings, while Opus One averages 4.7 from 978 ratings.
Do Calendars or Opus One have ads?
Neither Calendars nor Opus One shows ads.
Which is updated more often, Calendars or Opus One?
Calendars ships an update weekly, and Opus One every 3 weeks. Most recently, Calendars was updated on October 28, 2026 and Opus One on October 26, 2026.

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