This app was mentioned in 2 comments, with an average of 2.00 upvotes
Dots Online
Brings back memories of playing this at the back of the classroom
https://play.google.com/store/apps/details?id=com.byril.dots
Also by same author:
Sea Battle 2
https://play.google.com/store/apps/details?id=com.byril.seabattle2
If you're interested, there are versions of the game available for Android and iOS. Could be useful for getting into the game and quickly learning the rules.