Calki vs MainframeMonitor
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
Calki
This app combines a powerful camera number scanner, a full-featured unit converter, and a beautifully designed calculator. It allows you to scan numbers from documents, convert units across various categories, and perform calculations with live previews and advanced history.
- Camera number scanner (OCR)
- Unit converter with 12 categories
- Smart calculator with live preview
- Advanced calculation history
- Customizable themes and fonts
- Ad-free experience
Read full descriptionHide full description
A REFRESHING EVERYDAY CALCULATOR I started this because every calculator I'd ever used felt exactly the same, a grid of grey buttons, technically functional, completely uninspired. You look at this thing dozens of times a day. I figured it might as well feel good to use. DON'T TYPE IT. SCAN IT. The part of daily maths that actually annoyed me wasn't the maths, it was the typing. Squinting at a receipt, a packing slip, a utility bill, trying to get a long string of digits into my phone without fat-fingering a number along the way. So I built real-time number scanning into Calki. Point your camera at any printed digits and they drop straight into your live calculation. No re-typing, no silent typos. SCAN ON AUTOPILOT: OP MODE Even scanning one number at a time felt too slow once you're working through a long list of expenses or measurements, so I added OP Mode. Turn it on and Calki keeps adding (or subtracting, multiplying, whatever operation you need) every number you scan, one after another, as fast as you can point the camera. No tapping the plus sign between items, just point, scan, and watch the total build. TOTAL EDITING FREEDOM I never liked that most calculators punish a tiny mistake by making you start the whole thing over. So in Calki, your equation is never locked in. Made an error three numbers back? Tap it, fix it, or remove it outright. Swap an operator mid-calculation without losing your place. It's your equation, you should be able to touch any part of it. FLUID, CUSTOM CONVERSIONS I got tired of jumping between three different apps just to convert a price, check a weight, and finish the maths. So the converter lives right inside Calki, built for speed: glide between units and categories in a single tap. And if you've got something specific to your own world, you can build a custom unit for it. A HISTORY LOG WITH MUSCLE Nothing winds me up more than digging through a buried menu to find yesterday's calculation. Calki's history stays close and stays useful: double-tap any entry to drop its result back into your current calculation, long-press to pull the entire original expression back onto the board, or add a note so you remember what a number was even for, weeks later. RETRO FLAIR, MODERN SOUL Last one is just personal taste. I don't think calculators need to look clinical and forgettable. Calki's design is inspired by the kind of premium, classic hardware I'd actually want sitting on my desk, and the themes are fully customisable if your taste runs differently from mine. The buttons on the Retro and Industrial themes in particular took a lot of obsessing over. I wanted them to feel like a real high-end device in your hand rather than a flat picture of one, so each was built with realistic animation, haptics, sound, and design to back it up. Thanks for reading this far, and hope you give Calki a try. It's a one-person project, so every download, review, and bit of feedback genuinely reaches me, personally. Terms of Use (EULA): https://www.apple.com/legal/internet-services/itunes/dev/stdeula/
MainframeMonitor
Transform your iPhone into a vintage mainframe with a nostalgic CRT display. Monitor live system stats like battery, CPU, and memory, all within an authentic retro console experience. Includes hidden classic text-based games.
- Live system monitoring (battery, CPU, memory, storage)
- Home screen widgets
- Authentic CRT effects (glow, scanlines)
- Retro boot sequence
- Hidden classic text-based games
- Customizable color themes (Green, Amber)
Read full descriptionHide full description
Turn your iPhone into a mainframe from the golden age of computing. MAINFRAME MONITOR shows your device's live stats wrapped in a nostalgic CRT console – complete with phosphor glow, scanlines, a boot sequence and satisfying key clicks. Choose between classic GREEN or warm AMBER, each with its own matching app icon. ■ LIVE SYSTEM MONITOR • Battery, CPU, memory and free storage • Uptime, network status and device info • All in real time, right on the glowing screen ■ HOME SCREEN WIDGET • Keep your key system stats always in view • In the same retro CRT style ■ REAL MAINFRAME FEELING • Authentic boot sequence on launch • Scanlines, glow and CRT effects • Terminal-style PF function-key controls ■ HIDDEN CLASSIC GAMES • Snake, Hamurabi, Void Patrol and Bagels • Text-based retro games, just like on the old terminals ■ FAIR & PRIVATE • Completely free • No ads, no trackers, no accounts • All data stays on your device Whether as a stylish system monitor, a home screen widget or a hands-on piece of computing history – MAINFRAME MONITOR brings back the charm of the old data centers. Made with attention to detail. Be sure to check out my other apps right inside the app.
Screenshots
Verdict
The clearest difference is in-app purchases: MainframeMonitor at none against Calki's 3. MainframeMonitor also leads on ads (none vs shown) and rating (5.0 vs 4.8). Calki's advantage is ratings volume (16 vs 1). On price, update cadence, device support and iOS requirement 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
Both are free to download. Calki sells 3 in-app purchases, starting at $0.99 per month. MainframeMonitor asks for nothing beyond the download.
MainframeMonitor holds the better App Store score, 5.0 against 4.8. That said, the two scores are not equally well evidenced: Calki has 16 ratings behind it against 1, so its average is the more settled of the two.
Both ship on a similar rhythm, roughly fortnightly. The most recent releases landed on October 25, 2026 and October 24, 2026 respectively.
| Parameter | Calki | MainframeMonitor |
|---|---|---|
| Price | Free | Free |
| Rating | 4.8 (16 ratings) | 5.0 (1 ratings) — better |
| Positive reviews | 100.0% of reviews | — |
| Number of ratings | 16 — better | 1 |
| Update frequency | Fortnightly | Fortnightly |
| Ads | Yes | No — better |
| In-app purchases | Yes | No — better |
| Monetization | Ad-supported | Free — better |
| Devices | iPhone, iPad | iPhone, iPad |
| Requires iOS | 18.0 | 17.0 — better |
| Further details — not scored | ||
| Size | 52 MB | 24 MB |
| Age rating | 4+ | 4+ |
| Developer | Vimal Parthan | Ralf Langhoff |
Customer experience
Calki
MainframeMonitor
In-app purchases
Calki
- Calki Pro Monthly3 Days trial$0.991 Month
- Calki Pro Yearly7 Days trial$2.991 Year
- Calki Pro Lifetime$5.99
MainframeMonitor
No in-app purchases









