Ubuntu
From OpenSimulator
I'm trying to have opensimulator in the Ubuntu universe repositories and some suitable source packages have being created yet. If you want to install them for testing just:
Copy the lines below and add them to your system's software sources.
deb http://ppa.launchpad.net/shankao/opensimulator/ubuntu karmic main
deb-src http://ppa.launchpad.net/shankao/opensimulator/ubuntu karmic main
Then, you can use your preferred package manager (i.e. synaptic, apt-get, aptitude) to install the program, marked as opensimulator-server.