Parts Of Speech Tagger. This is a tool for helping learners parse sentences correctly. It can be particularly useful for natives of languages that have different word order to English, or where subjects and verbs are not separate entities for example.
Paste in a chunk of text and you'll get loads of useful information returned about: length (syllable count, word count, average sentence length), readability (using common scales) and a CEFR level recommendation. Useful when you've found a text you think you'd like to use in class.
For those annoying times when you have a word on the tip of the tongue but you just can't remember what it is. Also doubles as a thesaurus. It's also really easy to use.
A great tool for class preparation. Paste/write in a sentence containing your target language, and the Scrambler will mix up the words for you to use on a worksheet or however you decide.