The definition of a Limulus is as follows:

1. Uses standard hardware off the shelf hardware and allows for both file system and compute node expansion;
2. Uses an Open Source cluster software stack that contains an integrated set of software packages to manage the cluster and create and run software. The software stack must run on top of existing Linux distributions;
3. Consumes less than 100 watts when idle and less then 1000 watts when fully loaded;
4. Has a power supply efficiency above 80% to reduce heat
5. Has a noise signature that is acceptable in a modern office environment (less than 45dB).
6. Achieves a price to performance of less then $100(US) per GFLOPS

As you can see some of the design parameters are rather loose allowing design flexibility, while others are very tight providing desktop/office functionality.