Shuush is a web-based Twitter client that allows you to focus attention on the people that tweet less frequently.
Twitter users are assigned a frequency level of 1-11, calculated as a function of how many tweets per day each user has averaged since joining.
A simple on/off switch allows you to flip between normal and amplified views, the latter giving a visual boost in text size to those infrequent but valuable tweets that often get lost in the firehose. The updates of less active tweeters are scaled up whilst more active tweeters are scaled down, making it easy to retrospectively scan the tweetstream of people you are following for those rarer communications.
This is a really useful tool, for dialling down the level of frequent updates and surfacing the missed messages, to achieve the balance that Twitter currently lacks. It would be great to have a way of doing this with hashtags too.