Infinite Responder is an autoresponder script that is free to download.
Since it’s a script, you have to host it on your own domain. This has some advantages, since all the links involved are to your own domain. But, you have to install it and configure it. The author has an installation service if PHP and MySQL isn’t your thing. He charges $30 for the installation. If you don’t have much experience with PHP and MySQL, I’d recommend paying for the installation.
Infinite Responder allows subscription via email. Email subscribers will be sent a confirmation message to ensure they really do want to subscribe. Configuring this is a little bit more involved than with hosted autoresponder services, since you also have to create the email account.
You can customize the thank you page with Infinite Responder, as well as customizing the page they see when they unsubscribe from your newsletter. You also get complete customization of the confirmation email.
Delivery rate is okay, I’ve had some of the confirmation messages flagged as spam in Gmail.
Infinite Responder allows for sending broadcasts (called bursts) to all subscribers. Text and HTML emails are supported throughout.
Link tracking is not supported, so if that’s important to you you’ll also need an ad tracker.
Overall, the feature set in Infinite Responder is quite good, but it’s a little harder to use than most hosted autoresponders. I’ll give it a B+ for features, and an A+ for value.