"OMake is a build system with a similar style and syntax to GNU make but with many additional features, including support for large projects spanning multiple directories, default configuration files simplifying the standard compilation tasks, support for commands that produce several targets at once, fast, reliable, automated, scriptable dependency analysis using MD5 digests, portability, and built-in functions that provide the most common features of programs like grep, sed, and awk. It also provides active filesystem monitoring that restarts builds automatically when source files are modified. A companion command interpreter that can be used interactively is included."
Also appears to offer some degree of parallelism (though it claims not to work with NFS):
-- Ian Holmes - 16 Mar 2007