Aren't they on github? https://github.com/Homebrew/homebrew

They used to use SourceForge to distribute bottles (binaries), but have switched to Bintray a while ago.

Do you know anyone else who uses bintray? I'm considering hosting downloads for the open source projects I maintain with them, but never heard of it much before.

Off the top of my head I recall only Vagrant (https://bintray.com/mitchellh/vagrant/vagrant)

For some odd reason, when I try to do 'brew upgrade tmux' I get the error 'tmux 1.9a already installed.' I want to upgrade to tmux2.