Looks like a viral license that would prevent this being used in any closed-source applications: http://www.ravenbrook.com/project/mps/master/license.txt
If the licensing terms aren't suitable for you (for
example, you're developing a closed-source commercial
product or a compiler run-time system) you can easily
license the MPS under different terms from Ravenbrook.
Please write to us <mps-questions@ravenbrook.com> for
more information.
I was excited to use MPS in the runtime of an open-source compiler, but if users of the compiler had to pay in order to use it for closed-source apps then that would be a big turn-off.