Adobe Flex is an open source platform that allows you to create RIA (rich internet applications) easily that can run on all browsers and uses the Adobe Flash Player. This platform is of special interest to Salesforce users because Salesforce provides a flex toolkit that eases integration between Flex and the Salesforce APIs.
Adobe provides a easy to follow course that will get you up to speed with Flex at Flex in a Week.
Salesforce developers can go to the ADN website to learn more about integrating Flex with Salesforce.
