I discovered Open Food Facts very recently. I was supersurprised because the mobile app is very neat, and I didn’t expect there would be so many products (edit: in Spain). I’ve sent two contributions so far.
Also, you can download their database. If I had some time, I’d try to run some queries on it. (I’m on a low sodium diet and sometimes you find the most unexpected products with little salt, but it’s time consuming.)
edit: also, I forgot, the app is on F-Droid, another nice touch.
Running LanguageTool locally is a bit of a pain, with some manual steps. Plus you have to fetch some data files. You can find around a few projects like this one to make it easier to run LanguageTool.
And yes, as the poster mentioned, LanguageTool keeps some code exclusive to their paid version. There’s a bit of a tension because they ask people not to extend OSS LanguageTool with their paid features.
There’s also this interesting clone, but it seems abandoned.