Freespace 2 was widely regarded as the best space sim ever made and killed the genre when it didn’t do as well as expected. It ended on a cliffhanger. About 10 years ago the rights to the IP were sold for only $10,000.
I used to love bzflags. It’s still being developed and it’s a great game. I just wish it was modernized a bit more. Maybe easier wan/lan especially for people without access to their routers.