I want to request that CT implement LanguageTool, an open-source proofreading tool already available in OmegaT.
I second that.
It is java-based and works for OpenOffice/LibreOffice, so its implementation might be less painful than any other tool (I say this without having any idea, sorry).
Half of it is already there: Hunspell. The other half is questionable, but can be accessed in LibreOffice/OOo, Vim, or downloaded as a desktop app.
Indeed the other half may be questionable, but this will depend mainly on your language. German is rather good, but not perfect (compared to MS Office). The desktop app (at least the version I know) is rather crappy, allowing to copy, paste and then check sentence by sentence.
The API use with LanguageTool has been extended. Indeed, there were and there are some possible user scenarios for the rookies:
The simple use (up to 2500 ch. per check) is free, the paid use starts with 19 € per month. Quite good results for German.
Advanced users, don't forget: you can set up LT on your own server, but the API fot CafeTran is still missing.
And no, it is not about being free, open source does not mean free like free beer.