From the website: 

Conversate is really an experiment. We think a lot of people feel frustrated trying to have group conversations over e-mail, and Conversate is one way to reign in the problem. We’re very interested in your feedback on this beta version.

Here’s how it works: simply fill in the title of a new conversation and enter the e-mail addresses of whoever you’d like to talk with. Your group will receive an e-mail invitation to join, and by clicking on the link they’ll be brought to an online discussion space for whatever you want to talk about. Your conversations can be public or private, and Conversate is free.
We think it's better than group e-mails because your friends and family won't get annoyed with inbox clutter. Plus, nested comments are way more legible than a bunch of people trying to quote each other in replies.

Once you create a Conversate account, there are a number of ways to make it even easier to have conversations online and stay in touch. You can subscribe to an RSS feed of new messages in different conversations, or if you prefer the old-fashioned way, you can receive e-mail alerts of new messages.