This project has been around for a while, since about 2001 when their site used to be just a collection of links pointing to our beloved hvac-talk.
The authors do credit much of their learning experience to this site.
This will compile and run on a *nix platform. The page also has links to other open source projects that can be compiled and run on a Linux machine.
Here you can find source code for home automation. Might be fun to play with.
This is geared more towards SCADA but like any other automation system can be used for building automation (my opinion).
There are a lot of open source projects in various stages of development that will compile and run on a Linux kernel. Also, most any Java based automation system will function under Linux so long as it will run the JVM.
Welcome to the *nix world What distro did you happen to choose?