FLAIM is a very scalable, quite fantastic database technology. However, it is sorely neglected outside of Novell / Attachmate. This Cool Solution is an effort to make it slightly more available by fixing some problems compiling it on OS X. The original source had accommodations for OS X, but there were compilation errors which I have fixed in this fork.
Novell / Attachmate uses FLAIM as the basis for eDirectory GroupWise. Additionally, the Church of Jesus Christ of Latter-day Saints has used FLAIM in its legendarily large genealogy recording.
The main page for the open source FLAIM is at http://sourceforge.net/projects/flaim/ Unfortunately, both the maintainers have left Novell and so the Sourceforge page is stagnant, which is why this fork exists instead of simply submitting patches. It is worth noting that FLAIM is very much in active development inside of Novell, but copying new work over to the open-source branch is not a priority. That said, the core of the code has not changed as it is a mature format.
All the documentation you could ever want is on the original SourceForge page. There is also very good documentation included with the source.
I have not yet gotten XFLAIM (FLAIM 5.x) compiling on OS X as it is not a priority for me -- although it has a few modern advantages over existing FLAIM, my interest is understanding the FLAIM 4.x branch as the classic technology is more relevant to my work life.
If you are compiling FLAIM on non-OS X Unix or Windows, you are probably better off just using the original source without my changes, unless you encounter compilation errors in which case some of my light work might be valuable.