spaCy is another active open source (MIT) POS-tagger. 
In a previous discussion on HN[1] it was well received.<p>There is a simplified educational 200 lines python version [2] of it. It claims 96.8% for the WSJ corpus.<p>What am I missing here?<p>[1] <a href="https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=8942783" rel="nofollow">https:&#x2F;&#x2F;news.ycombinator.com&#x2F;item?id=8942783</a><p>[2] <a href="https:&#x2F;&#x2F;spacy.io&#x2F;blog&#x2F;part-of-speech-pos-tagger-in-python" rel="nofollow">https:&#x2F;&#x2F;spacy.io&#x2F;blog&#x2F;part-of-speech-pos-tagger-in-python</a>