I thought it would be a good idea, to collect opened/open source game codes that could be used as resources (unlikely as SCP has a rather restricted license, but it might be worth a look) or as inspiration to see how other games implemented various ideas:
Item 1: The Homeworld source codehttp://homesource.nekomimicon.net/
Obviously this game vastly had different priorities, but unlike most of the engines out there it's a space simulator. What might be of particular interest is how multiple textures and animation were handled in this code. It was also very script intensive, so it might also contain ideas on a scripting system.
No actual implementation can be used from this source (Relic put even more restriction on this than Volition did on FS2), however this game did a lot of stuff well and the source could be definitely worth a look for inspiration.