HootSuite is great, but it's also quite a hefty tool if all you need to do is let people tweet on behalf of n accounts. Also HootSuite works really well if you have a small team of people managing your social media but breaks down (or becomes expensive) if you need to give access to lots of people (this is where you end up with systems involving sharing lists of passwords!).

The idea behind Echelon (and its pricing model) is to promote sensible account security around the simplest of actions - tweeting. The bigger your team the more you pay but otherwise you can divide up your accounts however you want (different amounts of access for different people, etc).