Longtime Ensō user here. Your update to query interest in a Linux version has given me hope. The last thing someone actively trying to avoid distraction needs is an open browser window!
Consider this:
cat > ~/my-notes.txt <<EOF Type here anything you want. To save and finish, type: EOF
Consider this:
Zero software to install, no editing except maybe backspace, no selection, no spellchecking, no formatting, no distractions on the screen.