LanguageTool is like Grammarly, except completely free and open source. (I will be adding it to the resources page later today) It’s written in Java which means it is quite performant.
There are plugins to use LanguageTool in:
- Google Docs
- and standalone desktop app
What I like is that there is a Python library, grammar-check, that interfaces with LanguageTool. You can get up and running and start checking grammar on your own with Python scripts. There’s also a Ruby library but it only uses the API from the website. The Python library uses a locally installed version of LanguageTool so you don’t have to rely on an internet connection (very useful for me when I’m writing on the train or bus for example).