After years of waiting for Google to tie its disparate communication services together, the company has today announced, at Google I/O, a unified messaging system simply called Hangouts, available for Android, iOS, and the web using the Chrome extension. The new app will be available today on all platforms.

The new service, which adopts the name of one of Google's most popular and beloved products, replaces Google Talk, Google+ Messenger, and the original Google+ Hangout video chat service — Hangouts will eventually replace all of Google's communication properties. The new Hangouts is basically a messaging app, in the same realm as WhatsApp and Facebook Messenger, but with some of its own twists.

The Hangout app will present users with a list of recent text conversations instead of a contact list; rather than something like Google Talk, this has more mobile messaging DNA. Each conversation gets its own name, like a chat room, and can be labeled with an image or one of Google's new emoji. (Google says it has created 850 new hand-drawn emoji for Hangouts.) Hangouts will store all conversations in the cloud, and allow users to message friends at any time, even if they're not connected. Users can visit past conversations and access shared photos and video call history; thanks to Google's cloud, Hangouts will sync everywhere, giving people access to conversations on any device.

True to the original Google+ Hangout service, the new Hangouts allows any conversation to become a video call with up to 10 friends. "We want to fill in all the boxes so people can just focus on the obvious, which is just hanging out," Google's Vic Gundotra said on stage today at Google I/O 2013.

Part of that focus on "just hanging out" includes a new "watermark" feature that allows users to show when someone else is typing, and indicate how far others have read in a conversation. As noted in our exclusive preview of Hangouts, the watermarks create a sense of immediacy that's missing from regular text conversations, allowing you to see who is available or away at a glance — but the "active / away" presence indicators you may be used to from Google Talk have been replaced.

Google has also integrated Google+ tightly into the new Hangouts experience, and one of the most useful new features is automatic photo saving. Every photo that you or a friend posts in Hangouts will be automatically saved in a private shared album on Google+, and users can view the photos they've shared over time.

Google Voice will also be integrated into Hangouts over time, but Google has not yet provided a timeline for integration. The service is also missing other features users may have come to expect in other universal messaging platforms, like SMS support.

Read More: Exclusive: Inside Hangouts, Google's big fix for its messaging mess