Going away? Gmail can respond automatically to your emails, but not your chat messages. Autoresponder can fill the gap.
Have accounts that foward email that you never log into? You could be missing chat messages. Autoresponder can tell people how to get in touch and let you know about incoming messages.
Switching from Google Hangouts to something like Slack? Autoresponder can tell existing contacts where to find you.
Want autoreplies on multiple accounts? No problem; you can attach them all to one Autoresponder account.
You can receive emails when messages are received so you don't miss a thing.
Autoresponder can only access your chat messages, and will never use them for anything other than sending replies.
Normal conversations won't be interrupted: autoresponses are only sent when you're offline or away.
Autoresponses can be configured to fire as often as you'd like and even handle contacts specific differently.
Contributions welcome! And if you have your own server, feel free to self-host.