Btpd is a utility for sharing files over the BitTorrent network protocol. It runs in daemon mode, thus needing no controlling terminal or GUI. Instead, the daemon is controlled by the btcli command line utility or other programs capable of sending commands and queries on the btpd control socket.
SALI (Sara Automatic Linux Installer) is a tool that allows you to install Linux on multiple machines at once. It support several protocols for downloading by way of aria2 to install a machine. For example, BitTorrent and rsync are supported. SALI originates from SystemImager and still uses the same philosophy. It is a scalable method for performing unattended installation. SALI is mostly used in cluster setups.