Automatic tweet for free

Tweet

I have heard that we can schedule the automatic Tweet on twitter since is not only used to share a personal tweet updates, but also updates on product launches, events, news and others. To be able to automate the update status updates via scheduling can be a very helpful thing.I have seen web service like stackroll able to do that,it was free service and able to stack contains an update to our followers up to 30 tweets. It can also use for shortcut link our sites. StackRoll is free to use buddy schedule a status update on Twitter.However, I have seen them still at Beta version.. I think if we can do update or tweeting automatically it will be great for our needs, either for business or for personal.. What do you think? Do you have any other recommended automatic tweet sites for free?