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.
U.D.O.S. zero is a minimalistic C, ASCII, VRML, non-privileged User Distributed Operating System.
A simple-to-use ERP and CRM.