Starbase 999 is a Star Trek freeform writing RPG, commonly referred to as a Simm. It is based in the Andromeda Galaxy (read our intro for a little insight into how we got there), and it will include several other sci fi elements as it progresses. We have a wiki that will explain many of the elements, so don't worry about not knowing much about the added tech.
SGACC is a more traditional Stargate simm. It runs in an alternate universe where the Stargate program didn't have Daniel Jackson to uncover the secrets of the program, so it got a much rockier start.