The Open Build Service (OBS) is a generic system to build and distribute binary packages from sources in an automatic, consistent and reproducible way. You can release packages as well as updates, add-ons, appliances and entire distributions for a wide range of operating systems and hardware architectures.
The openSUSE project runs it's own instance at https://build.opensuse.org
Tools around OBS
Here is a list of official and non official OBS components and tools.
The OBS is documented in this wiki. Packagers should start reading the tutorial and the cross distribution package how to. Some general hints can be found on the FAQ and Tips & Tricks pages. There are various presentations available. An important piece is the documentation for the API. The API is a simple and generic interface to work with the Open Build Service. You may use it to integrate your tools to submit code updates, check the current state of your projects or doing something very different and cool.