LanguageTool is an open-source tool for checking the text for spelling and grammar errors. Currently, it supports more than 20 different languages including such less popular languages as Slovenian, Swedish, and Polish.
LanguageTool supports many popular writing applications such as LibreOffice, Microsoft Word, and Google Docs. It also has plugins for Firefox and Google Chrome. Also, there is a plugin for Thunderbird.
Reference: https://languagetoolplus.com/
