I've used Cleverstack throughout its testing and beta stages. It's been an incredibly helpful tool for when I just need to think and jot down my thoughts without as much concern about layout or order. Then it's a helpful place for me to re-prioritize what it is I'm actually thinking, and how I'll end up executing on that thinking.
Unless I absolutely have to, I will not sign up to any service that forces me to use these two companies for login.
When you dump a bunch of designers on a simple idea, you get a super well designed and fun to use app, that's helpful too!
This is a very well crafted product that I love using on a daily basis!