Compton is a compositor for X, and a fork of xcompmgr-dana (in turn, a fork of xcompmgr)
Bugs were fixed, and some features added.
Fixes from the original xcompmgr:
* fixed a segfault when opening certain window types
* fixed a memory leak caused by not freeing up shadows (from the freedesktop repo)
Changes from xcompmgr:
* inactive window transparency (specified with -i)
* titlebar/frame transparency (specified with -e)
* menu transparency
* shadows are now enabled for argb windows, e.g. terminals with transparency
* removed serverside shadows (and simple compositing) to clean the code, the only option that remains is clientside shadows
The above features give compton a feature set similar to the xfce compositor.
Compton's frame transparency should work with any window manager that properly sets _NET_FRAME_EXTENTS.