Is that in addition to any other retirement/pension money for federal employees?
Yes/no. It's in addition to our pension for FERS employees / military. Basically the fed.gov equivalent of the 401K. Up until this year, it was somewhat limited in how you could take out the dough, but it is more like a 401K now in that regard.
Uncle sugar contributes 1% to the TSP for FERS employees whether the employee participates or not. This is to give them parity with CSRS employees (an old pension system that was stopped in the 80s - employees at the time were grandfathered in). CSRS employees don't get the employer contribution (because their pension is better - I think it's the same for .mil), but can still participate in the TSP. For FERS employees at least, if you participate, the gov matches the first 3% and then gives you a 50% match for another 2% (or vice versa - I always forget).
It also has probably the cheapest fees out there.