# Delta Theta Lambda vs OPIN (Open+Invitation)

The clearest difference is in-app purchases: Delta Theta Lambda at none against OPIN (Open+Invitation)'s 1. Delta Theta Lambda also leads on iOS requirement (13.0 vs 15.1). OPIN (Open+Invitation)'s advantage is update cadence (every 8 days vs every 41 months). On price, ads and device support there is nothing between them.

Both are free to download. OPIN (Open+Invitation) sells 1 one-off in-app purchase. Delta Theta Lambda asks for nothing beyond the download.

Delta Theta Lambda ships an update every 41 months, OPIN (Open+Invitation) every 8 days. The most recent releases landed on September 14, 2026 and June 27, 2026 respectively.

## The numbers

| Metric | Delta Theta Lambda | OPIN (Open+Invitation) |
| --- | --- | --- |
| Price | Free | Free |
| Rating | — | **[5.0 (4 ratings)](https://appshunter.io/ios/app/opin-open-plus-invitation/id6760378331/reviews)** |
| Number of ratings | — | **4** |
| Positive reviews | — | 100.0% of reviews |
| In-app purchases | **No** | Yes |
| Ads | No | No |
| Update frequency | Every 41 months | **Every 8 days** |
| Monetization | — | Free with in-app purchases |
| Size | 24 MB | 31 MB |
| Requires iOS | **13.0** | 15.1 |
| Devices | **iPhone, iPad, iPod** | iPhone, iPod |
| Age rating | 4+ | 17+ |
| Developer | [Ricardo Cumberbatch](https://appshunter.io/developer/1455104172) | [Connor Loretz](https://appshunter.io/developer/1881310218) |

## What reviewers say

### Delta Theta Lambda

[App page](https://appshunter.io/ios/app/delta-theta-lambda/id1595860513)

**Features:** macOS Compatibility

**In-app purchases:** none


### OPIN (Open+Invitation)

[App page](https://appshunter.io/ios/app/opin-open-plus-invitation/id6760378331)

Easily share open invitations for local events like garage sales, parties, or pop-up shops. Post your event on an interactive map, set the time, and let nearby users discover it. Users can add events to their calendar with one tap.

**Highlights:** Interactive map of local events, Post events with location and time, Discover nearby invitations, One-tap calendar sync, Private event invites, Filter by category and date

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Post an Opin | $0.99 | one-time |


## Frequently asked questions

### Is Delta Theta Lambda free?

Delta Theta Lambda is free to download, with no in-app purchases.

### Is OPIN (Open+Invitation) free?

OPIN (Open+Invitation) is free to download, with in-app purchases available.

### Do Delta Theta Lambda or OPIN (Open+Invitation) have ads?

Neither Delta Theta Lambda nor OPIN (Open+Invitation) shows ads.

### Which is updated more often, Delta Theta Lambda or OPIN (Open+Invitation)?

Delta Theta Lambda ships an update every 41 months, and OPIN (Open+Invitation) every 8 days. Most recently, Delta Theta Lambda was updated on September 14, 2026 and OPIN (Open+Invitation) on June 27, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*