I pass mine to kids, try on projects etc.
I have an E6300/Asus EPU MicroATX/4gb PC6400/350w psu/Samsung F3 drives/Fractal 1000 case system which was for playing with different server OS's such as Windows 2012 and Amahi. This will probably end up with the 120gb SSD running Ubuntu.
Kids had the old Q9550/Gigabyte P45/8gb PC8500/Sammy F3/HD 4870 GPU system.
This will end up in a new Fractal R5 most likely, with a new SSD and all my old HDD's, possibly as a server or general PC for all the family, and if I get a new pair of GPU's it will get one of the 7950's.
I had an E8500/Asus Maximus II/4gb Dominator GT/HD 5750 passive/GD02 for an HTPC, then with a single SSD for XBMC.
That HTPC has now been put in a spare TJ08B-E case with a spare HD7950 so I can try Windows 10. This will have the HD-5750 put back in, and the 120gb SSD replaced with a 240gb, and go into the kids room. It will get a 7950 if I get new cards.
I have a couple of older machines, one of them was a mint old biege PC tower with Windows 98. I was silly enough to wipe Windows 98 off the drive, just to find the old motherboard will not recognize a DVD drive. It had one stick of ram, but I found 2x1 GB of Corsair PC3500LL to use in that.
Now stuck without an OS on that, though the wife wants it out as she thinks it's junk.