Aside from the obvious, like Wiktionary, Duden, there is also:
- Verbforen – generates German verb forms using smart rules. Proprietary.
- OpenThesaurus – mostly synonyms, German.
- bab.la – verb tables in different languages, proprietary.
- Morphologie-Lexikon – generated using Morphy.
- Wortschatz Uni Leipzig – SOAP API, pretty scientific dataset.
- Wordnik – closed db, supposedly from Wiktionary, API, English only, interesting API Showcase.
- LanguageTool – Open Source style and grammar checker, with a builtin database.
Attempts to parse Wiktionary (collected from SO)
- Dbnary (open, multiple languages)
- wiktionary-parser (open code, unfinished)
- jwktl (open code, seem quite extensive)
- wikokit (open source, Russian and English)
- perl-wiktionary-parser (English only)
- dbpedia RDF extraction (open code, seemingly API in the future, declarative extensions)
Part of Speech tagging