mcwm is a minimalistic window manager implemented using XCB. It doesn't use libX11 at all. It is a traditional floating window manager with no fancy smarts like those in modern tiling window managers.
xombrero is a minimalist's Web browser. It strives to be vi-like and is suited for heavy keyboard users.
A tool for figuring out who pays what to whom after a series of transactions among members of a group.
An advanced multi-threaded file manager.