At its I/O developer gathering in San Francisco this week, Google offered more details about Android and Google Web Toolkit, while also opening up access to "everyone" for its new Google App Engine hosted development environment.

Not at all surprisingly, Google is delivering at least two conference sessions specific to Android, a controversial open source platform aimed at helping developers to create mobile applications that will interoperate across handheld devices from multiple vendors.

But other conference fare includes, for example, "Rapid Development with Python, Django and Google App Engine," "Getting Started with Google App Engine -- On Your Mac," and "Extend the Reach of Your Google Apps Environment with Google APIs."

Rolled out in mid-April, Google App Engine is a cloud-based hosted development environment, designed to let developers build applications on the same infrastructure that fuels Google's own applications.

"The goal is to make it easy to get started with a new web app, and then [to] make it easy to scale when that app reaches the point where it's receiving significant traffic and has millions of users," maintained Paul McDonald, a Google product manager.

More than 150,000 developers have signed up for the App Engine over the past six weeks, with most of them landing on a waiting list. But Google announced yesterday that, starting today, a free preview edition of the engine will be available to everyone, with no wait required.

As of about 3:15 pm PDT today, the App Engine download site still told visitors that it was only available to the first 10,000 developers who signed up for the software.

"[But] sign-ups [were] OPEN to all as of this morning (PT)," a Google spokesperson told BetaNews. "The language you saw on the site is old and will be updated shortly. You should be able to sign up [already] despite the language."

The preview period is expected to end later this year, according to Google officials. Until then, developers are required to stick to a "free quota" consisting of 500 MB of storage, and enough bandwidth to support around 5 million pageviews per month.

Google has also announced pricing for after the free preview period ends. Pricing will be based on CPU core-hour, outgoing bandwidth, incoming bandwidth, and monthly storage capacity.

But as McDonald wrote in his blog in mid-April, the preview release "is by no means feature-complete." Google is still seeking feedback from developers on what to include in the final release, BetaNews was told.

In the weeks ahead, Google plans to release new image-manipulation and memory cache APIs for Google App Engine.

In addition, Google is now targeting later this week for the availability of Release Candidate 1.5 of the Google Web Toolkit, a Java-based environment that enables developers to write applications in Java that are compiled into JavaScript and deployed through AJAX.

Google Health is one recently introduced application built with Web Toolkit. As previously reported in BetaNews, Google CEO Eric Schmidt told medical practitioners at a health care conference in March that third-party developers are also creating specialized applications for Google Health, a Web-based "cloud" initiative envisioned as storing consumers' health information online.

New features in Toolkit 1.5 will include Java 5 language support, a faster compiler, and more software libraries to help with building AJAX apps.

Special conference sessions are also on the agenda for YouTube and Google Maps development. Google's OpenSocial API sandbox, just rolled out last week, is also sure to be a topic of conversation at Google I/O this week. The sandbox is intended to guide developers through the process of building and distributing interactive gadgets.

Facebook, Google's competitor in the social networking space, yesterday countered Google's OpenSocial efforts by acknowledging that it will now convert its own social networking code base into an open source platform.

"The major social networks are competing for the attention of the developer community, as the moves by Facebook and Google clearly show," said Ri Pierce-Grove, an analyst at DataMonitor.