Oh all right, but these are not free.
www.digifish.us for AquaReal, the best 'Aquarium' style saver around.
www.simaquarium.com, via Digital Illusions, another series of 'Fishy' ones, and of course, www.SereneScreen.com for the second-best 'Marine' saver and their equally nifty 'Goldfish' bowl.
You do need some serious grunt to run them as well.