ROS is an open-source, meta-operating system for your robot. It provides the services you would expect from an operating system, including hardware abstraction, low-level device control, implementation of commonly-used functionality, message-passing between processes, and package management.
Setup Notes - Groovy
Currently, groovy is the only (semi-)supported ROS release that has Arch packages. The core, comm, and robot variants have meta-packages that should install all the necessary packages:AUR, AUR, (TODO: robot metapackage). In addition, AUR (along with its dependencies) has a package. Beware, the dependency tree goes at least five levels deep at times. AUR handles it OK, AUR falls flat.
The packages are all available in the maintainer's github: arch-ros-stacks. Not all packages there are in a working state, so use with caution. Please, report any issues with the packages on their respective AUR pages.
Usage Notes - Groovy
Due to the fact that Ubuntu and Arch handle the python2/3 binary split differently, catkin_make[_isolated] will not work on its own. To use these commands, create the following aliases in your ~/.bashrc (or equivalent):
alias catkin_make='catkin_make -DPYTHON_EXECUTABLE=/usr/bin/python2 -DPYTHON_INCLUDE_DIR=/usr/include/python2.7 -DPYTHON_LIBRARY=/usr/lib/libpython2.7.so' alias catkin_make_isolated='catkin_make_isolated -DPYTHON_EXECUTABLE=/usr/bin/python2 -DPYTHON_INCLUDE_DIR=/usr/include/python2.7 -DPYTHON_LIBRARY=/usr/lib/libpython2.7.so'
Without these lines, cmake will default to python 3, which you don't want. It is also possible to simply add the defines into any call of catkin_make[_isolated] (which you have to do if you want to call those commands within a script).
For further information on how to use ROS, see the ROS Tutorials.