Music, recording, mixing, re-mixing, plug-ins and gear @ home studio environment.
Mac Pro 1.1 2006. Quad 2.66GHz, upgraded into Mac Pro 2.1, 2 x 3 GHz Quad-Core Intel Xeon 8 Core CPU with 16GB of RAM.
Trying to squeeze out as much resources I can from those old machines because they can be bought second hand for very little money nowadays and they are very stable workhorses.