Do you really think your followers are checking your tweets? Many of us wasting our precious tweets unknowingly. Now we’ll see when the people following you are active on Twitter, so that your shared links
and tweets can get popular. By this you can establish your Twitter Existence.
When to tweet analyzes the time at which your followers tweet and gives you a personalized recommendation on when the best time of day for you to tweet is. Amazing to see Whentotweet is built in Python on top of Google App Engine.
The free version of When to tweet analyzes your first 500 followers and the latest 200 tweets of each follower and the PRO (premium) version analyzes one million followers and up to 1000 tweets per follower.
Reference : hellboundbloggers.com