I am looking for an application that acts as a stack exchange client, typically on the desktop.

Features:

- Can ask/edit questions
- Can answer questions
- Can comment
- Supports MathJax

Nice to have's:

- Support for close/open/delete/flag questions
- User stats page
- Moderator tools
- Offline support

I am interested in applications that run on any of the following systems:

- Windows 7
- Mac OS X
- iPhone
- iPad
- Ubuntu