Bump bc of curiosity and if it works in x86 better, i have some spare computers and would like to help some mesh network
you could try the basic ones first (Tor, Freenet and I2P)
Do you want proper meshnets or just, networks. Tor is not really a meshnet at all, (not that you cant use it on an rpi, I do). Freenet and I2P are also pretty much overlay networks, riding ontop of the internet and pretty reliant on it.
Other things include for example hyperboria. But outside of specific geographic regions this isnt a valiable (also perhaps freifunk, but same thing). All those could howerver, also be run on a raspi to my knowledge.
You could start a meshnet of you own. But you will probably want far more than one rpi in that case.