Google's new "Wave" service, announced in May, is to open to the public in a controlled beta program in September of this year, it's been announced.

Wave combines instant messaging, email and sharing functionality to create a potentially powerful open-source communications tool, and autumn access will be offered to those who have pre-registered for the service.

In a blog post Google has said: "We plan to start extending the Google Wave preview beyond developers on September 30th. This will take place on rather than the separate 'sandbox' instance we are currently using, and we plan to involve about 100,000 users".

Early Google Wave APIs have also been revealed with "Groupy-the-bot" offering users the ability to create groups and manage their own subscriptions and "Waves in WordPress" described as "a neat use of the embed API that makes it easy to put waves in a post or page on WordPress".

Leading up to the semi-public rollout, Google says it's "focusing on improving the speed, stability and usability of Google Wave". We will keep you posted.