More info from Cooler Master: http://coolermaster-usa.com/microsite/hafstacker/
It uses a rail system that allows you to expand and upgrade components via a chasis system. So lets say you want to have multiple PCs in one unit for a LAN party or one massive PC or BOTH! It has two stacker components with a front PSU and a rear PSU. The rear PSU allows for more higher end CPU Coolers such as the Hyper 202 and V8 GTS. When October 15 rolls around you will have a choice of the HAF 935 configuration with the HAF 915R and HAF 295, Mini-ITX HAF 915R and the Mini-ITX 915F. These different configurations allow you to easily attached and detach more stacks at will. This is the perfect opportunity for home theatre computer builders who want to have the main system in one stack and then expand to a second stack with all the hard drive storage. The HAF Stacker series is the very first of its kind and will be very popular in the computer building community (water and air cooling).