Ever thought about creating a totally silent computer? Turn old PC into a quiet network router, or media player, or thin terminal client? Among all you need a solid-state (i.e. containing no moving parts) hard disk drive.
"Real" high performance SSD drives used in enterprise applications are very expensive and you most likely have no reason to pay that much for extra performance you don't need - in many cases price of "real" chip drives defeats purposes of creating an SSD-based machine. For newer motherboards it is possible to use USB sticks available now at every corner. But what if the computer has no high speed USB port, or can't boot from USB? Then you can use Compact Flash! It is essentially old good IDE hard drive interface with much more compact connector. So it is possible to convert a CF card into IDE disk via an inexpensive adapter. It also usually gives much better performance than you can get from USB sticks. Virtually any PC (even old 286's and 386s!) has an IDE controller and any OS since MS-DOS 3 (IIRC) can boot from an IDE hard drive. The other reason to use CF may be that you (or your friend) might have some surplus card left after upgrading a card in digital camera.
CF to IDE adapters are quite hard to obtain in local stores but fortunately they are easily available by an order via Internet. Here are two adapters I purchased (almost for peanuts) in a Chinese online shop called Deal Extreme. This is the first version:
Both adapters work like a charm - just insert a card, set Master/Slave jumper, connect the adapter to IDE data cable and floppy power cable, fix it inside of computer case via electrician tape or hot glue. And voila, your computer got a solid-state IDE drive. You can partition and format it using standard software (e.g. fdisk and format), install any operating system and so on.