Looks like it's just a libpurple plugin, and should work in Adium as well. He's even got a .dylib build in the Makefile, but I can't get it to build after tinkering with it for a few minutes. Oh well.
The way the GitHub page is set up is weird. Basically two different plugins are hosted on one repo. The root tree you linked to has the original client required plugin. Go under "Skypeweb" folder and you'll see it's an entirely different plugin that you can compile and don't need a client (also has its own README).