See the introduction and documention in the wiki.
Implements some of the taskbar extensions discussed at, msdn.
Requires the threadFunc class, note that taskbarInterface.ahk includes this file, manage directories.
There is an example usage here.
A real use example is showcased in wolf_II's very nice app, Anagrams (v2.13+, requires the Additional files.zip file.)
Note: file names appended with _v2 are for AHK v2.