I only have one monitor and one keyboard, but other than that, I have three complete machines. My main machine is a 1.33 GHz T-Bird. My second machine is a 650 MHz original Athlon that is almost fully up to date, except for current files and a some current updates on the OS. I keep it because it's a great backup if my main machine fails, and I still occasionally need to test one of my GFD's.
Then, there's my little putt-putt 486 DX6/100. It runs DOS 6.22 and Win 3.11 very well. It's great for setting up DOS based industrial control programs, including some that crash on faster machines, and, in a real pinch, it will also run my DOS based schematic and printed circuit layout program, as well as Office 95 for Win 3.x. It isn't worth enough money to sell, it's too slow to give away, even to newbie kids, and it doesn't take up that much space, so there's no point in trashing it. 🙂