I am in the planning phase of a new multi-user client/server app using Flash via Flex and AIR. I am trying to decide which web platform/stack is the best suited for this?
I have used RoR in the past, but as i understand, RoR is single-threaded, and is therefore not the ideal choice for handling potentially thousands of simultaneous requests.
I have done some reading about Scala and Lift and that is an intriguing option, but i was wondering if there are other languages/frameworks out there that would work well for my project?
i don't know too much about the Scala and Lift ... if you wanna stick to ruby, check out merb ... it seems it will be merged with RoR anyways, so you could maybe just wait for the next version ... :)
you might want to take a look at Haxe (a high level language, that targets many platforms, as AVM1, AVM2, PHP, c++ ectc.) and neko (a server VM available as compiler target for Haxe), as well as Haxe remoting (you can simply compile your Haxe net-code to an swc and stick to AS3/mxml for the rest) ... neko scales quite well ... it's very light and extensible ... there are many ways of using it as server platform, but it also allows you writing everything from scratch, since the API exposes low level access ...
edit: you should rather use mod_tora, since it has lower footprint ... for the other things mentioned, just check out the mailing list ... there is a "simple persistent objects database" layer, that could help ... also there is some "full persitent objects database" floating around ... and for routing, there are also multiple solutions ... don't forget to check out haxelib ... you can find quite a lot of reusable stuff there ...