PostPost creates a searchable index of your Twitter stream that lets you look for tweets by term and then filter results by specific Twitter account. This can be helpful if you're trying to find a tweet that you sent last year or, even tougher, a useful tweet that you know you saw a while back, but can't remember from whom. Or, perhaps you're researching a new subject and want to see what some of the smart people you follow on Twitter have had to say about it over the past few months.