I'm in the design of a complex app. I want to provide a cross-plataform
solution (that its, Windows(or .NET), Linux, Web).

My main concern now is the client part.

My first inclination is build 1-3 GUI clients (Win/Linux/Web), but this can
overkill my plans...so i think in unify the client in the Web side. However,
my kind of aplications is the worst for put in Web Client..is like a ERP,
with (maybe) grapics, validations build for the end-user, dinamic creation
of the forms, etc... Think now in the something close to a POS for the kind of user interaction....

I'm coding a similar solution (other ERP) and use ASP.NET. The server-side
is fine but the client-side is a nightmare, because the interaction is soo
slow (however my boss like that)... The stateless nature of the web and the
limited HTML tool-set is overkill enough for a user for consider not usable
my kind of app...

So, i want to know if exist a kind of replacement of the HTML good enough to
emulate a fast native GUI, in a cross-over way...I'm not afraid about install a plugin, but i need thta this work over Windows&Linux(other OS are not enough common in my country)

My first tentation come to Flash, but i'm not sure, or i don't know. I require the capability of build anything in runtime, and need merge it in the whole solution (like html generation is merged in ASP.NET)