One of the new features of the upcoming AbiWord 2.4 is the English grammar checker based on Link Grammar a free software syntax analyzer for English. But here comes the question:

Does anyone know a grammar checker for other languages, like German, Spanish, French, etc. that would be available under a Free (free software) license?

There used to be a proprietary French grammar checker named Correcteur 101, but since 2003 it is no longer developed on Linux for Intel (I think they also had a PPC version).