LICENSE: GPLv3
Process controller (with extra features!) in a window.

Author's comments:

The #defines for header files start with "_" which is bad practice. Well, there's probably many other bad practices there but that's the obvious one that I noticed when glancing at the sources.

One possible problem is that it seems Slayer's UI was created using Attila Mezei's "Interface Elements"... I don't remember the details about that UI toolkit.