I can very much second the “Otherland” series. I’m not much of a fantasy fan (and can’t manage to sink my teeth into Williams’ other series because of that), but I found Otherland to be a very enjoyable and memorable series. Definitely worth it just for Otherland.
For somewhat larger projects, I think the OS Haiku is a perfect example. It isn’t a benevolent dictatorship, there is no single leader — there are just long-time contributors. If you send in contributions substantive or regular enough, there’s a good chance you’ll get push access. Patches generally are accepted with open arms, and devs with push access give constructive criticism on patches kindly. The OS is better for it!