Freespace space combat sim series has remained a cult favorite for many PC gamers over the years. Many have wanted to see a third game in the series come out at some point. As it turns out there are some folks at the game's original developer Volition that feel the same way. In a chat at NowGamer, Volition producer Jim Boone is quoted as saying, "There is a group of people (at Volition) that would commit murder to do that game."
The original Freespace (full name Descent Freespace The Great War) was the first ever game from Volition and was released in 1998 via publisher Interplay. Its space combat gameplay and its impressive (at that time) graphics won over game critics and fans. A sequel, Freespace 2, was quickly developed and released in 1999. However that game didn't sell as well. According to Boone, part of the reason was that by that time PC games controlled by joysticks were no longer being made.
The Freespace IP is still owned by Interplay but Volition was later sold to THQ so any chance of a Freespace 3 made by Volition would likely come if THQ were to buy the rights from Interplay. Meanwhile you can get the first two games via GoG.com. In addition the source code for Freespace 2's graphics engine was released in 2002 and is the basis for several free downloadable PC games made by amateurs.