Futz.me is a multi-channel communication and reminder tool that runs from the address bar. You can send texts, emails, Twitter messages, bookmarks, and many other options. Skimming the front page and the FAQ give you a real feel for what this service can do.
What strikes me as the bread and butter innovation is the Chrome extension that allows you to send a message to another user that pops up on their Chrome browser as a notification. You can message yourself to test it out or send me (dbin78) something.
It appears that testing is still in the very early stages. I do not see any user limits on the test so give it a try by signing up and downloading the Chrome extension. Their Twitter account is @Futzme. I believe this will be a hit with the tech crowd, but to get mainstream use a bit of a UI needs to be built and an option to reply on the extension notifications. They started the service in 2009 and this is a great next step for them.