When I was a teenager I had a friend who wanted to build a PC on a very limited budget, and she wanted it to be able to play The Sims 2. Well after much bargain hunting and throwing ideas around, we couldn’t find a way to afford every component we needed, but we were close, so we decided to forgo a case! Just put the motherboard on the desk with other components arrayed around it. Cables everywhere. The tricky part is we had no power button, but I showed her which pins to sort out with a paper clip, and it worked great.