What's the best writing tool you've ever found?

LyX, hands down.

Grammarly and Quilbot

Grammarly. Nothing more reassuring than having a near faultless piece of software check for typos and mistakes rather than having to reread my work 3 times over.

Grammarly & Wordtune :)

I'm also using Grammarly :)

Quillbot & LibreOffice