Both OpenLaszlo and the official Flex SDK are open-source, so basically any good text editor (I'd suggest FlashDevelop on Windows or VM) or IDE can be used to create full-fledged ActionScript projects. If you're mainly interested in point-and-click, design-based environments, though, you may find yourself limited to the relatively expensive Adobe Flash IDE. There have been a few attempts to create alternative IDEs, but (in my opinion) none that come close to offering a full authoring environment. (Check osflash.org for other possibilities, though.)
If none of these options fit your needs, and you just want to make something quick and simple without investing a lot of time and effort, you may find it best to simply hire a freelance developer/designer to create the piece you need.