How Do You Repurpose Old Hardware?

I repair computers for a living, and I often get people trying to dump their 6-8 year old computers onto me. In the past this used to be fine as I could re-purpose them for simple web browsing etc. for schools or older folks, but it seems that in the past few years there has been such a surge in demand in what a computer can do that none of these older PCs are viable anymore.