Advice needed - Best Ajax UI Frameworks?

[eluser]Randy Casburn[/eluser]
@nmweb, @bnewton, @the_ancient,

Reference ExtJS Licensing...

Let me clarify for everyone: IMHO solve the entire "My, oh My, there's a license in my eye" dilemma by purchasing the commercial license. The perceived problems evaporate.

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Oh whoops, there I go again, crossing that domain between "for commercial gain" vs. "for community benefit".
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I don't recommend distributing commercial apps with ExtJS using the GPLv3 version because of the viral nature of the license. If you're looking for a Freebie you should look elsewhere.

Here's an interesting API with an compelling visual design tool. It just is not mature/stable enough for me to recommend: Sigma Visual Builder
The link is to the visual builder, but there is a complete JS API behind it too.

If you want to take advantage of other's work and not have to pay for it, this API is licensed under LGPL if I recall.

Randy