Sure :) Github name is Silasary.

And TeamCity is fine.

There's http://sparkle-project.org/ for OSX (and it's associated Windown port http://winsparkle.org/)

Windows has ClickOnce (As you already know), and I have a [rather rudimentary] OSX/Linux implementation of it, if you want to go down that road. (https://bitbucket.org/Silasary/clickmono)

For Linux solutions, it's easy enough to set up a Continuous Integration server to create .deb files. (Which will hit anyone on SteamOS, and a good chunk of other Linux users)

And yes, there's always the option of rolling your own updater. (But I'd recommend away from that one - They end up being really gross: https://github.com/silasary/simpleupdate/)

If we want to keep in in C#, I'd recommend using Mono.XWT, a framework that abstracts and uses WPF, Cocoa, and GTK to allow a singular codebase to look native on Windows, OSX and Linux.

I'm a developer who frequently works with Mono and OSX.
More than happy to help with the Mac Client.