I think DVUI [1] is zig's most mature UI framework, and I have been enjoying using it for a while.

Fizzy is just one project that's pushing zig's desktop app dev story. They recently integrated another open source project velopack [2] and while that part isn't in zig (everything else is), this project has almost everything I'd want from a non-toy electron application. Autoupdating, cross-platform, native macOS context and topbar menus, etc.

1: https://github.com/david-vanderson/dvui

2: https://github.com/velopack/velopack