Write a cross platform easy to set up and use peer code review software (take hints from CodeCollaborator theirs is good but expensive). It should have hooks into Git/SVN and be easily extended in the future to include other version control systems. It would also be cool if it had the ability to have source code scanning plugins like phpcs (code sniffer) or phpmd(mess detector)... I'm a PHP guy you can tell, but I'm sure the guys from the java, c++, and other communities could use similar tools. Make sure it has an easy to set up web interface (you could package a webserver into the deal that listens on whatever port is configured during the setup process).