Apple has launched a version of its web browser Safari for Windows, competing head to head with Microsoft's Explorer and Mozilla's Firefox.
Thousands of developers are attending the conference
Chief executive Steve Jobs said Apple "dream big" and wanted to expand the 4.9% market share Safari enjoys.
Mr Jobs was speaking at a conference of developers for Apple products in San Francisco, California.
He said Safari was "the fastest browser on Windows", saying it was twice as fast as Internet Explorer.
A test version of Safari 3 for Windows XP, Vista and Apple Macs running OSX, is available for download from the Apple website. Apple is hoping to replicate the success of iTunes, which has proved enormously popular on both Macs and Windows machines.
"We think Windows users are going to be really impressed when they see how fast and intuitive web browsing can be with Safari," said Mr Jobs.
Mr Jobs used the conference to lift the lid on new features of its forthcoming operating system (OS) for Macs, called Leopard.
He said the OS has 300 new features and demoed 10, including a new organisational system for the desktop called Stacks and a new folder system which lets users browse files and applications visually, just as music lovers can browse album covers in iTunes.
He also unveiled Quick Look, a feature which lets users preview files, such as movies, photos and documents, without having to open up a related application. For example, users will be able to preview a movie file without having to open up QuickTime.
Leopard is due for release in October and will cost $129 (£89).
JupiterResearch analyst Michael Gartenberg said the new features would give developers "the tools to create the next generation of applications".
Writing on his blog, he said: "Apple has once again taken their platform to the next step and given developers the framework they need. It also looks and feels really cool and perhaps that's even more important."
Mr Jobs also gave the greenlight to third-party development of new applications for its forthcoming iPhone mobile phone.
In a u-turn from a previously stated policy, he said developers would be able to build web applications for the device that "extend the capabilities of iPhone... but keep the iPhone secure".
Instead of having to test each and every new application themselves, Apple will allow developers to build web applications for the phone which run inside the device's web browser Safari and which were built on existing web standards.
Games giant Electronic Arts were also on stage to announce a series of titles that would be released for the Mac.
The latest Harry Potter game, Battlefield 2142, Tiger Woods, Need for Speed Carbon and Madden are all to be released for the plaform, in major boost to gaming on Macs.
Games legend John Carmack, of Id software, also announced that the firm was working on an un-named project for Apple Macs, as well as other major platforms.