Currently your best bet is Unigine. Currently it has better engine but worse tooling than Unity and a 12 month license is in the same ballpark as a Unity Pro License. You probably want at least one programmer in your team if you go this route though. I will say that Linux is absolutely a first class citizen as an Authoring platform for games. I have about 5 years experience Authoring using Unigine on Linux.
If you don't have a coder or the cash and you can hang in there for about a month LeadWorks is in the process of porting. As far as I can tell they are aiming for something similar to Unity. I put money into the kickstarter and am waiting for my copy before I can say more about it.