Not community, but there is http://cert.startcom.org/ .

You can also do your own (OpenSSL has everything you need).

And for a community one, you'd still need a verification mechanism and a protection mechanism for the roots; both of which could be hard to do in a volatile environment. http://www.cacert.org/ Seems to be that, don't think they are included in any browsers by default though (it's not in mine at least).