nncp [1, 2] is probably the best Sneakernet tool I've found. It's very UNIX-y which makes it pretty hard to operate if you're not technical but would also make it pretty easy to wrap around with a UI. You have to explicitly add a list of "neighbors" to your configuration and you can send "packets" either by spooling to file or using a TCP/Noise connection. You can also send data hop-by-hop and is e2e encrypted.