From the README on github:
momcom is a command-line tool for Mac OS X that takes an uncompiled Core Data model created with Xcode and compiles it to produce a compiled .mom or .momd suitable for use at run time.
Please note that momcom is experimental. Although it is intended to be at least as as functional as compiling a data model using Xcode’s built-in model compiler, it is not mature enough to recommend as a replacement.