Grammarly: I discovered it last year and I’ve used it daily since then. It activates on every textarea, highlighting every grammar and spelling mistake. The double-click for synonim features is also really useful. With the premium version, it highlights even more advanced issues, like passive voice sentences.
Hemingway App: it’s an editor that helps you write readable content. In many ways, its features overlap with Grammarly, but for longer content I use both.
Ludwig: it defines itself as a smart translator and linguistic search engine and it really is. The best thing about this app is that you can search by examples. You can enter an English sentence, and it will search for similar ones in its sources. A recent addition, but very valuable.
In fact, I’m trying to improve my writing with this blog. ↩