I guess that would be Clem, who seems to have done all the commits. I don't think he has time for detailing it though
Having a look at the code, the primary code is in usr/lib/linuxmint/mintWelcome/mintWelcome.py (code in usr/bin is just the wrapper launcher for this). Glade provides the UI I think, so you need that. The code, except for check of your system to enable/disable some optional elements on the Welcome Screen (like upgrade from cd to dvd version), is pretty straight forward.
Do you mean to improve it, or use it for something else?