OverSIP runs on Linux/BSD based operating systems (also in OSX starting from OverSIP 2.0.0) with the following requirements:
Ruby >= 1.9.3
Version 1.9.3 or above required (Ruby 2 versions are also valid).
It can be a public IPv4 and/or IPv6. Read the F.A.Q. entry Running OverSIP Behind NAT if you want to run OverSIP behind NAT.