What does HackerNews think of transmission?

Official Transmission BitTorrent client repository

Language: C++

Are you sure? I don't recall it using GTK3 on Mac.

> A native Mac OS X GUI application

> GTK+ and Qt GUI applications for Linux, BSD, etc.

https://github.com/transmission/transmission

In my opinion, here is how I would handle this:

Use git and not mercurial. Use github over Source Forge. This will get you more eye balls on the project. Developers are more skilled in git than mercurial as well.

- Create a core in C that handles all the base functionality of the email client

- Create a UI for each platform using its native toolkits. Cocoa for macOS, MFC/.Net for Windows, GTK+ etc. You want the client to be native to the platform so it feels natural in all UI aspects and integration with the underlying OS.

I believe Transmission takes this approach and it seems to work well: https://github.com/transmission/transmission