While it is tempting to look for a "free download" link for OMSI 2: Steam Edition

If you are looking for the ultimate technical bus simulation experience, OMSI 2: The Omnibus Simulator

You can download OMSI 2 Bus Simulator from the following sources:

Manage ticket sales, adjust the heating for passenger comfort, and handle realistic mechanical breakdowns.

Once you own the base game, you can expand it for free by visiting community forums like OMSI WebDisk Steam Workshop