From OLPC

Minimal Linux distributions strip Linux down to a set of elements that can run on computers with reduced capabilities. Some are targeted at old computers. Some are targeted at embedded systems built into machinery, vehicles, home appliances, PDAs and mobile phones.

Available for OLPC XO

Not known to be available for OLPC XO

We did have a long list here, when we were choosing technologies for development, but the list became out of date, and there's no advantage to doubling up on information that can be found in DistroWatch or Wikipedia, so please use those sites: