I am enamored as of late with the Achates Power entry that is gaining steam. Their model is along the lines developing the architecture and technology and licensing it to any manufacture to do so, and they seem to have a lot of suitors lined up. An Opposed Piston 2 Stroke Diesel for starters. But they have gone after tweaking the porting w/ CFD as well as the pistons bowl shapes, I am impressed. I am equally impressed with the vertical layout and using a Roots Blower for External Scavenging for charging. I stumbled upon how Roots blowers in particular multiply torque in gobs at the low end. Paxton's and Turbo's can't compare. Tangent to this they didn't go with a stepped piston of other internal charging and it's problems.
Go here: http://achatespower.com/our-formula/opposed-piston/
Being an airplane nut, the Junker's Jumo engine was on my radar screen, and I had the pleasure of meeting an author that helped get it their. However, of all the inventor opposed engines out their I think this one has a shot at making it.
Now a Barrel ( Dyna-Cam type ) opposed piston is an interesting proposition, their is one out their....