These are the binary packages for ROS 2 Crystal Clemmys Patch Release 4 (2019-04-08)
For runtime dependencies see the binary package installation instructions.
Your system must be up-to-date to be compatible with the downloaded packages.
Additionally there are Debian packages for Ubuntu Bionic.
Note: ignore the Source code links, because they don't actually contain the source code for ROS 2 (they're auto-generated by GitHub). Instead, grab the binary package for your platform. If you're interested in building from source, consult the building from source instructions.