My personal NUR repository
It provides a pre-compiled binary cache for NixOS unstable.
To configure Nix manually, add the following to your nix.conf:
substituters = https://nix-cache.unixpimps.net/ijohanne
trusted-public-keys = ijohanne:55EJTBFbq5pCYx2tf+aR8pmVPvCmP7QlafHH90/kikw=