One of these days I’ll try Zeta on my old Amd 300 mhz desktop:
ZETA is a very fast operating system written from the ground up to get more out of your hardware than any other. With a true micro kernel is of only 640 KB and a 64-bit journalling filesystem to make things fly. Never before was it so easy to create MP3′s or encode and decode videos. Never before was it so easy to partition a hard drive or create CDs. Needless to say, ZETA is also virus-free leaving you to concentrate on getting things done.
From what I could read in the review, this BeOS package is a nice bet to bring old computers back to life.