SimMars Beta 3 is in the works and coming closer to packacking stage before release.
The main part of new content is new buildings, there are more than 100 new buildings of all kinds! And we're still adding more before the release. There will also be a seperate SimMars launcher so you can play SimCity 4 and SimMars with a single click.
We are looking for modders who can help with replacing the transit elements (ie. rails, vehicle models etc.).
Head over to our forum at Simtropolis if you want to help.
Below are preview pictures of some of the new buildings: