Automating Twitter tasks is a controversial topic. There are those who say you should never do it. At the other extreme there are tools that promise to get you thousands of followers in no time (which, IMHO, is utter nonsense). Twitter itself prefers personal, direct communication but understands that automation is warranted under certain conditions as long as the Twitter rules are not violated.
New automation tools are released all the time. Here is another one, Autotweeter. Like all tools it does have its uses and also its faults. Read more here about Autotweeter and a tool to help you protect yourself against spamming robots (the latter, TrueTwit, is listed in the “Really Useful Twitter Tool Box”).