OKRStudio - Connect Trello cards to OKRs. Manage OKRs inside of Trello
Lifetick - Lifetick is an online Goal Setting application with a stylish, easy to use interface.
OKRs.app - Reach your personal goals with OKRs
Beeminder - Beeminder
Perdoo - OKR methodology, software and coaching
Joes Goals - Joe's Goals is an online goal-tracking website. 100% Free. No Download Required.