Actual Battlestar Galactica games have been pretty awful. Most fan-made mods never end up being finished. But Diaspora, one of the more promising attempts to put players in the cockpit of a Viper (or a Raptor), has actually made it to the finish line, and is now available for download.
You should get it. Now. Because it's fantastic!
Having been in development for four years, it's built on the bones of classic old space shooter Freespace 2, but you won't need the original to play it; everything you need is in the one download, which you can get free of charge from the project's site.
It's not without its share of problems - like an excruciating tutorial - but stick with it and you get an authentic Battlestar experience many AAA developers would struggle to attain. The first time you shoot out of a launch tube into a sea of Basestars and missiles you'll have to work hard to get the smile off your face.
Diaspora has both a singleplayer campaign and multiplayer, as well as an included mission editor. You can get it for Windows, Mac and Linux at the link below.
Diaspora [Release Build]