Spheres is my main science-fiction gaming setting (trying to figure out what you call this sort of thing is a bit of a headache). I guess you could say I started writing it in about 1993, when I started to brew some ideas about cyberpunk in combination with star-spanning communications. I've been developing it, in one form or another, since then.
Spheres is set in the year 2221 CE (or AD, if you prefer). Humanity has finally broken the lightspeed barrier, and has also discovered a handful of sentient races out among the stars. The area of space known to humanity, Known Space, is approximately 50 light-years in radius, roughly centered on the solar system.
I have tried to make the background pretty realistic, though with a few flights of fantasy (FTL starships being the main one). To keep it feeling real, I've often used real names, especially of countries and companies. These are intended in no way to make fun of or slander the parties mentioned; they are mentioned in satire only.
Spheres is also an RPG. I've only run it a few times: a small campaign in Chinese, strangely enough, a PBEM and a small one-on-one adventure. The RPG's rules are highly based on HârnMaster, my favorite RPG of all time (well, with the possible exception of Spheres).
The main links for Spheres appear in the menu, which should be to the left. If you're not sure where to start, let me recommend the Spheres introduction.