Gaia is Mozilla's Phone UX for the Boot to Gecko (B2G) project.
Boot to Gecko aims to create a complete, standalone operating system for the open web.
You can read more about B2G here:
follow us on twitter: @Boot2Gecko
join the Mozilla Platform mailing list:
http://groups.google.com/group/mozilla.dev.platform
and talk to us on IRC:
#B2G on irc.mozilla.org
See INSTALL file in B2G repository for instructions on building and running B2G.