DCS World is an incredible study level combat flight simulator. It encompasses several maps, and a number of different aircraft modules to include jets, WWII birds, and choppers. It has been around for quite a while now and has a very significant following in both single player and multiplayer. It is continually updated and improved by Eagle Dynamics.
They recently introduced a Free to Play Program. For 6 months any aircraft module for a period of two weeks. After the initial 6 months again another 6 months - any aircraft module for a period of two weeks. Now this was announced on June 11th so that first month may already have passed not sure on that.
I have been a big fan of DCS since around 2008 and can tell you it is quite an amazing combat flight simulator. I have quite a number of hours in the F/A 18-C Hornet and love flying carrier ops with it. And yes it has native Oculus support along with Steam VR.