This is i2psnark, an I2P port of snark http://klomp.org/snark/ , a GPLv2 bittorrent client.
It contains significant enhancements including a web UI and support for
multitorrent, magnet, PEX and DHT.

i2psnark is packaged as a webapp running in the router console.

See http://i2p-projekt.i2p/en/docs/applications/bittorrent
or https://geti2p.net/en/docs/applications/bittorrent
for the specification of the protocols for bittorrent over I2P.