There are a number of Go programs available with Ubuntu. They can be installed either with "Add/Remove Programs" or with the "Synaptic Package Manager"
A partial list:
In addition, the following programs, though not included in Ubuntu's repositories, can be installed by following the instructions in their Sensei page.
Indigo - Download it from Bruno Bouzy's web site, and follow instructions for goGui similar to those for Mogo.
AmiGoGtp - Download from site, and follow goGui instructions.