Broken Gears (Cambridge University Roleplaying Society, 2005)
If the blurb is to be believed, the bulk of Broken Gears was written in 24 hours (by members of CURS). This is impressive. So is the book. (It's also free. http://www.r-hansen.com/broken/)
I'm not really a fan of Steampunk; all the other settings I've read seem to be horribly artificial in order to produce the suped up world and characters the authors wanted. They have never felt cohesive.
Broken Gears starts with the history of the world, rewriting history from 1940 to 2052 (and backhistory) in a wholistic and realistic way that makes good use known history to produce an anachronistic future. Large grokkable nations form in a coherent manner that lends to all the sorts of stories you would want to tell.
Mechanical technology and electricity are not founded on physics as we know it but by "chaids", spirits of technology. Technological achievements remain the same but the knowledge behind them is obviously quite difference. In 1944, Bletchley Park creates Colossus to solve the problems of the war. Once started, it creates superior radio-controlled war machines to win... but then never stops, leading to the War of Broken Gears.
In the aftermath, radio and electricity are forbidden. With the world in ruins and communication difficult, four nations dominate (the British empire, the United States, Russia/China and the independent Australia). I should add that this is a vast oversimplification, since these empires are definitely not cookie cutters and come with political histories that put everything into context.
The technology that's left is guns, large guns and massive guns. Giant war machines. And a thriving industry in innovative technology.
The basic system is a single page, although particular elements have their own section. There are five stats and 20 skills + any others you want to include. It is a simple roll under Stat+Skill-penalty (using a d12) with a minor but nice twist on critical successes.
This isn't a system you will take away but it's simple enough to just get on with. Combat is inevitable, but vehicular combat is encouraged (partly since healing is often tricky).
Most PC groups will be from a particular faction tackling internal or external challenges, e.g. working for British Secret Service or the Australian mercenaries. There are however options, especially in the US or the Buffer nations, for being ragtag groups facing a joint threat. The power level is low but can be increased through technology depending on the whims of the ST and players.
Many villains will be Other Factions or random bad guys; human enemies with human motivations. However, there are also powerful chaids determined to wreck the world - or those trying to summon demons of the same power level as Colossus.
Home produced, with some stock photos run through a filter. They may not reach the quantity or "fantasy" level of other Steampunk games but they fit the humanly anachronistic feel of the game.
Have I mentioned there is a rich history here?
While the stat choices are good, the skill list is fairly poor and awkward. While I have my doubts about a flat system, I couldn't really say more without testing.
The bigger problem is that it lacks pizzazz. What they have created is a pseudo-realistic setting, which is great, but people don't turn to steampunk for that. Two things that would help would be a more exuberent system (Adventure!, FATE or another pulp system would be fine) and some examples of exuberent technology (other than vehicles) which players may come up against or acquire.
The game leaves a lot to the imagination, but that is true of lots of similar games.