Nifty - Manage projects, work, and communications in one place.
OKRStudio - Connect Trello cards to OKRs. Manage OKRs inside of Trello
ZenHub - ZenHub is how the world's best software teams work together. Trusted by NASA, Docker, and Rackspace. Start free today!
OKRs.app - Reach your personal goals with OKRs
Intercom on Product Management - The ultimate resource for aspiring product managers
Perdoo - OKR methodology, software and coaching