Daniel Dura gave an overview of the AIR APIs.
Air provides a rich stack of APIs that is available to both Flash/Flex and HTML and runs on multiple platforms. These APIs cover: network detection, file I/O, custom window chrome, multiple windows, native menus, drag and drop with clipboard, system tray and dock notifications, application signing, application icons, file type registration, background applications, application updates, and network support.
He next drilled into some of the above areas in more detail. AIR specific classes are included in the Flex 3 documentation available on LiveDocs.
Windowing: Multiple window support, transparent windows, different window types (lightweight, utility, and standard), z-index ordering, and always in front.
Pixel Perfect: Alpha window overlay that shows width and height with no standard window chrome.
HTML Control: Integrated into Flash rendering pipeline (can apply effects to it), script bridging, and override default behavior (navigate, history, window, resize).
File I/O: Full read/write access, native file dialogs (save, select, select multiple, directory), and Async and Sync APIs.
Database: SQLite embedded database, zero setup, single file, and based on SQL92.
Drag and Drop/Clipboard: System level drag and drop (AIR to AIR, AIR to OS, OS to AIR, etc.), multiple formats (URL, files, text, serialized AS objects), and modifiers (link, copy, move). Drag and drop is handled through TransferableData objects.
Application Icons: No feed to know about icon format, can just supply PNG images.
Service Monitoring: Monitor network interface changes, monitor services, and extensible (supports multiple service types). URLMonitor class is one example.
Flex Builder: Debugging, code hinting, packaging, and application signing.