I have a few old PCs sitting in my study room. A Pentium 133 MHz and a Celeron 566 MHz.
The Pentium 133 MHz is probably of no use now. It is a small compact PC that I have assembled, probably the first one. That is the reason I am still keeping it. I will probably scrap it some day.
The Celeron 566 MHz is still working well with Windows XP, but a little slow. I have installed Filezilla FTP server, RealVNC in there, so converting it to be a file server. I have one problem to resolve though, it needs to be booted up without a monitor. I need to build a dummy monitor as suggested here.
There is also another Pentium 1.8 GHz pc that Mei Yu has left behind in Orhid park. The hard disk crashed, the RAM is only 256 MHz. Should be able to revive that.