Their website certainly doesn't make it easy to locate the source code (https://github.com/opf/openproject) or make it clear what license it's under (GPLv3). I had to navigate all the way to the manual installation guide to find a link to the GitHub.
It also isn't readily clear what the feature difference is between the community and enterprise editions. A feature matrix would be welcome here.
It does look like a really useful piece of software though.