I (tzlaine) am the lead developer, and I'm a professional C++ programmer. Our other main developer is Geoff, a grad student. We try to keep the quality of the code to a very high level. This is necessary for a project as big, complex, and ambitious as ours. We also use most of the "modern features" of C++, though certainly not everywhere. By "modern features" I mean things like templates, STL, and Boost. So, if you are already this kind of programmer and are looking for a quality project, or if you are smart but not that experienced, and don't mind learning a lot, this is your project.
To get a flavor for the project, here are the libraries we use: Boost (most of its libraries), OpenGL, OpenAL, GraphViz, Ogre, Ogg, Vorbis, OpenSteer, and GG. GG is a GUI library I wrote for OpenGL. You can find it on SourceForge. It has drivers for use with SDL and Ogre.
We are a GPL project, and we use the Creative Commons Attribution-Share Alike 3.0 Unported license for artwork and sound.
We have a website and wiki at http://freeorion.org , and a very active forum at http://freeorion.org/forum . Our code can be found on SourceForge too. Download the latest installer and have a look.
Here are some screenshots for our game to date:






We are currently working on our 3D combat system on a branch. Here are some screenshots of that. We have no ships yet -- like I said, this is what we're working on right now. However, you can see that we're serious about quality output, as well as quality code:






Those are placeholder planet textures. Higher-res ones are being made now. We have some very talented artists working on the project.