There are 2 repositories under threema topic.
Relay service for Threema Web push notifications.
The protocol used for communicating between the Threema mobile apps and a remote application (e.g. Threema Web).
Sekurŝranko, an efficient and memory-safe Threema Safe server implementation in Rust.
Gateway MsgApi SDK - PHP
WhatsAppChatBeautifier is a tool to render WhatsApp chats.
3ma Backup Viewer lets you view your Threema backup files.
Threema Desktop | Unofficial implementation of web.threema.ch into a Desktop Client using ElectronJS
Threema Gateway implementation for XenForo, offers two-step-authentication (or two-factor-authentication 2FA) for users
A sample web UI for the Threema Gateway using the PHP SDK
Threema Standalone Web App with Dark and Light Mode Support
Simple CefSharp Wrapper for Threema-Web including desktop-notifications.
Security Analysis of Instant Messaging Apps
A recipe for franz (https://meetfranz.com) for the Threema messenger
Gateway MsgApi SDK - Java
Chrome extension to apply darkmode on threema web. (outdated)
The Unofficial Electron Wrapper for Threema Web wraps Threema Web (a local copy of threema web is used instead of web.threema.ch) into an instance of chromium using electronjs.