WebTorrent Desktop is a bit abandoned, but last time I tried it, it still worked despite some warts (I think it wouldn’t work with newer Chromecasts).

My notes also have:

• https://github.com/asapach/peerflix-server
• https://github.com/hauxir/rapidbay
• https://github.com/anacrolix/torrent?tab=readme-ov-file#downstream-projects (This library is good at streaming, software using it should too)