You have a quite a choice as there are many vendors offering a range of different offerings. Here is a shortlist of just a few:
All of the above tools (perhaps with the exception of Betterworks) are great tools for managing OKRs for small and mid-size firms. When choosing a tool, I recommend looking for features for refining OKRs into initiatives, as more granular planning around goals provides a greater probability of achieving outcomes. Also look for features that encourage staff to keep their OKRs updated through regular check-ins. When you start using an OKR tool, the main benefit you will see will be through the increased transparency around goals that you engender into the organization and the increased communication that occurs around progress of goals across each team and particularly between employees and managers.
There are a number of OKR platforms out there. Betterworks, Perdoo etc. ZOKRI is OKR Software. There is a free plan for unlimited people and time. Also the is an AMAZING deal for start-ups which you can contact me about via matt[dot]roberts[@]zokri[dot]com.
The disclaimer is I founded this company. I am aware of my biases so I'd encourage you to try it out.
https://www.profit.co is a complete solution to define Objectives & Key Results (OKRs) at every level of your organization forcing you and your team to think before acting and a comprehensive system to measure progress on predefined frequencies to keep your company running like a well oiled machine towards your company’s goals.
We’ve just development a perfect tool for setting and tracking OKRs, it is really useful because we’ve involved lots of HRs and CEOs in the work on its usability and functional content!
if you are engaged, check Ahundred
Word of warning- despite the contemporary trendiness to speak about OKRs, I feel they do extra harm than appropriate if tied to bonuses. It's a rehashing of Drucker's Management by means of Objective article which comes out of the 50's and is not commonly used anymore.