Wikibase is the software behind Wikidata. It consists of a set of extensions to the MediaWiki software for storing and managing data (Wikibase Repository) and for embedding data on other wikis (Wikibase Client).
You can try out Wikibase by testing the demo system. If you happen to find bugs, please report them so they can be fixed before they hit Wikidata. If you want to work directly on Wikibase, several bugs are awaiting volunteers. For additional questions, please refer to Wikidata:Contact the development team.