The new lists feature (that was added to Twitter a while back) has made it easier for you to share your favorite groups of people, and track their tweets.  What Listiti brings to the table is free e-mail alerts when somebody, on a predefined list, references a keyword you wish to follow.

For example, you have a large list of every web host on Twitter, and you wanted to be notified when one of them mentions the word, “coupon”.  You would tell Listiti that your list was located at mitchkeeler/webhosts, give them the keyword, “coupon” , and then hand over your e-mail address you wish to be notified at. 

For the people who create the lists, they also provide badges for you to use to promote the lists you have created.  Overall, Listiti brings a few beneficial features to this new Twitter feature, that the Twitter team does not provide by default.