[tpaksoy]

There is the Brigade engine[1] that I know of. It's as far as I know a one man project. I haven't heard of an update in a long time though.

[1] https://www.youtube.com/watch?v=BpT6MkCeP7Y

[Gravityloss]

http://raytracey.blogspot.fi/

Sam Lapere seems to have left Otoy around November 2014.

[berkut]

I'd guess Jacco Bikker and Jeroen van Schijndel are still involved though?