What can i do with them ?

Hello there, i just found out that i have some 10+ blogger websites 8+ years old almost all are in the same niche, how do you think i could use them instead of just staying there ? Blog post to a new domain in the same niche ? Or maybe to start posting on them again ? Thanks

I'd update them and use them to link to my relevant sites.
But you'll need to revamp them first.

use them as backlink source.