How much of a C-MAX replacement is this really?
Only partial so far. C-MAX programs are fully supported for the Ocelot, but there is only partial support for Leopard-specific features. Also, interactive communication is limited to receiving notifications and sending X10 commands; Future support for getting and setting the variables, timers, and date/time is coming, but isn't there yet.
The front page says I can use this to build my own programs. How does that work? And how stable (or unstable) is this?
Most of the HouseMonkey code is fairly stable, except for the IDE code due to the number of features yet to be added. All code is in Java, except for the included RXTX library, which uses OS-specific code to communicate with the serial port. The easiest way to start your own app is to look at the files under the test/API/src directory; there are several JUnit test cases there demonstrate how to communicate with the Ocelot. I highly recommend using Eclipse for your development effort.
What's missing?
Most missing features (that I care about so far) have been added to the Bugzilla system for this project. Please add your own feature requests to the bugzilla, and I'll try to get to them as soon as possible.
How much does this cost?
It's free, under the terms of the GPL.
This code includes software written by the Apache Foundation.