It appears that a group of privacy enthusiasts run the servers. Here’s a page listing all their services.
There are also many other instances of Nitter.
More About The Nitter Interface
Nitter is an open-source alternative to Twitter’s interface.
Nitter’s advantages are:
- Lightweight (profiles pages tend to be 60 KB instead of 600 KB)
- The client never talks direct to Twitter
Nitter has several browser extensions maintained by the community.