knapsack[1] and knapsack_pro[2] are both under MIT license and seem to have the same code. How do you keep companies/people from using the pro without paying?
It works similarly like tools for exceptions tracking, i.e https://www.honeybadger.io is paid but has MIT client https://github.com/honeybadger-io/honeybadger-ruby
Other than that I do support paying customers.