App.net, Dalton Caldwell's proposal for a open developer infrastructure based on a paid model of users, won yet another note of approval Wednesday with the news that the makers of Tweetbot have developed an app for the network called Netbot. While App.net hasn't hit anything close to mainstream popularity yet — and isn't necessarily aiming for it right now — the fact that the Tweetbot makers have turned their talents to an App.net client just serves as further validation that Caldwell's efforts could have staying power.