I've been meaning to post about this for ages now, but I suppose it's better late than never...
Doc? is an AIR application that centralizes all of the help documentation in Flash and Flex (and indeed other documentation, if you want) into a single application. It's darned useful if you want to refer to the documentation without going to the online LiveDocs, or you want to check the documentation without opening Flash/Flex builder (like, if you're using FlashDevelop). On top of all that, the search is faster and often more accurate than the standard search facility, and the application also looks pretty damn sweet.
There's even plugins for Doc?, which add the the application search to the Flash IDE and Eclipse. - Which you can see how to install and configure from the plugins page. My only gripe with Doc? is that it has a bit of a user-interaction flaw - after you install the application, it's useless until you install the documentation. You can learn all about how to configure it from the Doc? FAQ page, and once you've done that it works - but for all the cleverness of the application, it gives you no guidance about how to get started, and you have to find it out yourself.
You can download Doc? from the //airdoc.be/, the dedicated website.