Adobe Animate
While not necessarily a development environment Adobe Animate is still a tool that can be used to develop AIR applications.
Code editing in Animate is not designed to facilitate application development but focussed on timeline animations and control. The above editors are much more fully featured and will make development easier.
Animate however is a very useful tool to have access to, particular for creating visual assets and animations for your AIR applications. Assets exported from Animate can be imported and used very easily in an AIR application.
Adobe Animate is available from Adobe as part of the Creative Cloud.