dkpro-jwpl
DKPro JWPL (DKPro Java Wikipedia Library) is a free, Java-based application programming interface that allows to access all information in Wikipedia.
Core features:
- Fast and efficient access to Wikipedia
- Parser for the MediaWiki syntax
- Language independent
In addition to the core functionality, DKPro JWPL allows access to Wikipedia's edit history with the Wikipedia Revision Toolkit.
Features of the Wikipedia Revision Toolkit:
- Tools for reconstructing past states of Wikipedia (TimeMachine)
- Efficient access to all article revisions (RevisionMachine)
- Dedicated revision storage format
More detailed information can be found here.