Google Developers Network is site for external developers interested in Google-related development. It is where we will publish free source code and lists of our API services.Some Google Open Source Project details can be found at http://code.google.com/projects.html but when logged in to your Google account you can start to enhance your website with an array of choices from embedding code on your site to making Google Gadgets
The Yahoo! Developer Network offers Web Services and APIs that make it easy for developers to build applications and mashups that integrate data sources in new ways, making the web a more useful and fun place for everyone. And the greatest thing of all it’s free for everyone to use. They also have a developers blog worth reading.
The place to start if your interested in using Microsfot products to create your next mobile application. Once there you can take part by joining the communnity forums or by posting questions or comments on the Mobile Web Team blog. They have a complete list of downloads and support there as well as a great learning center for soon to be MSN Developers.
A group of organisations including IBM, Mozilla, Zimbra and Dojo have announced a project to develop a common set of AJAX interfaces, plugins and widgets for Eclipse. The project is aimed at providing a common target for tools developers to support, as opposed to the myriad open source and proprietary toolkits and libraries available today.
You can read more on the Dojo projects site