As of now, there is a small core team of developers. If you want to get involved, please post an inquiry at the OpenMx developers' section of the OpenSEM forum. If you are interested in building OpenMx from source, take a look at the OpenMx Compilation How-To Guide. The project is licensed under the Apache License, Version 2.0.
OpenMx is licensed under the liberal open source Apache License, Version 2.0.