I'm in the middle of developing a CMS web app and I'd like to make it work well and look nice. Of course the age-old issues of browser support com into play here.
What are some good frameworks for developing "Web apps"?
I'm talking about libraries that do things that like AJAX, animations and HTML5 support.
Please provide link and description where possible.
EDIT:
To narrow it down a little bit (but only a little), I'm prefferably working with LAMP on the server side. HTML5/XHTML on the client.
Wow, impossibly huge question:
JQuery is probably your best bet on the client. It is a JavaScript library that makes pretty much everything easier.
You might also look at something like CSS3PIE.
Using HTML5 is just adding <!DOCTYPE html> at the top. After that, it depends what features you use.
Since you are "in the middle", I assume you do not need server-side help but who knows.
On the server, I would recommend you choose from one of three just to toss that out there:
There are thousands of options though. Probably the list of MVC frameworks is the shortest list to choose from: Click here to see a list of them on Wikipedia.
EDIT: I made my recommendation before the preference for LAMP was added to the question. I stick by my recommendations though. I use Linux, Apache, and MySQL myself but not usually with PHP. See the Wikipedia link for PHP framework choices.
I recommend using Unobtrusive JavaScript techniques as well.