The www.procode.org/stgit page is (freely) hosted somewhere in Florida and, because of the latest hurricanes, it's been down probably for more than a couple of weeks. I don't know when it will be up again.
The archives and the GIT repository are hosted in the UK and still available. For releases and snapshots:
http://homepage.ntlworld.com/cmarinas/stgit/
For cloning it:
git clone http://homepage.ntlworld.com/cmarinas/stgit.git
In the meantime, I will think about moving it to public source hosting site (like sf.net or similar).
-- Catalin