We're a few months away from introducing Tara premium, which includes access controls for teams and user level permissions (ie contributor, etc), and is based on simple subscription based pricing. It's pretty much what our users have asked for, and we're continuing to listen to their feedback.

That being said, our entire ethos is to have a functional free forever plan, where users can manage their tasks and run their sprints, without worrying about hitting a 10 user limit, limited-time trials or task limits. We're avid supporters of open source, and we believe closed source software should have wider availability. So much of B2B software is behind paywalls, demos and short trials, hence our approach.