MyMonero

MyMonero is probably the oldest third-party Monero wallet. It's available in a large number of different versions, see below. Its website is here, its collection of GitHub repositories here, its dedicated subreddit here.

Unlike most other Monero wallets MyMonero apps do not scan the Monero blockchain themselves by fetching blocks directly from Monero daemons using the Monero core wallet2 class, but they work together with a special backend that does the scanning for them, using the view private key.

The oldest member of the "family" is the web wallet that runs fully client-side in the browser. It's JavaScript code (and some WASM code?) that was written by hand in part and compiled/transpiled to JavaScript (and WASM?) from the Monero core C++ code in part by using Emscripten (see this repository).

The desktop wallet is built on Electron.

It's still to be found out what is the exact architecture of the iOS smartphone app and the Android smartphone app, but a first glance shows again heavy use of JavaScript and of course of the scanning backend.

From a technological point of view the web wallet might well be the most "unusual" Monero wallet in existence. Migrating the MyMonero wallets to Seraphis and Jamtis might bring unique and especially hard challenges.