Actually, Unicorn is indeed free (you can grab the code from git://bogomips.org/unicorn.git -- looks like it's GPL). FastCGI is an open specification, with many

Actually, Unicorn is indeed free (you can grab the code from git://bogomips.org/unicorn.git -- looks like it's GPL). FastCGI is an open specification, with many free implementations. There's definitely a lot of cool prior art in this space.