Hi Quentin, thanks for starting this!
I think this is a great chance to do an experiment and come up with a minimum viable product to keep track of OKRs. I’d certainly use that 
If this is something that people want and use (this could be part of the hypothesis), we could even go so far to include it in mozillians.org for example. Do you think it would make sense to come up with a hypothesis and validate it once people could test the MVP?
Regarding technology, I don’t think it really matters which technology to use for the MVP. Nevertheless I think it would be great if this would be a web app 
Looking forward to see what you come up with!
Cheers,
Michael