Nicotine is a feature-complete client for the SoulSeek filesharing network. You can use it to upload, download, search, and chat. You can keep a "buddy" list and basically everything else a SoulSeek client is supposed to do. If you are familiar with PySoulSeek, you'll probably notice a striking resemblance in appearance.
Skippy is a full screen pager for X11, not entirely unlike expocity and Apple's Expose. It arranges snapshots of all windows on the current desktop, allowing you to easily switch between applications. It doesn't require a specific window manager, but requires NetWM or GNOME WM specs compliance to work.