Currently, as Pijul is still in beta, the main channel to get it is the Rust Language package manager, Cargo. See here for installing Cargo (which comes with Rust), and then run the following command in your terminal:
cargo install pijul
nix-env -iA nixos.pijul
Package provided by Zygmunt Krynicki.
FreeBSD / DragonflyBSD
Major releases of Pijul are built for Windows, and available for download on https://pijul.org/downloads/#windows-binaries