Hello Abhi,

I suppose there is not manual way to test number of users can use the application at a time

You may use LOAD RUNNER. this software calculates the throughput of Bytes Generated per seconds for any application to x number of users.

to check the compatibility of web browser with web based application?

I think you mean to check browser compitablity of web application
user Firefox, Mozilla, Netscape, Opera, Safari, ie6, ie 7, and as many as you can. open any web application and check if the UI (User Interphase) is same as that for ie (Internet explorer) there are may plug in avalible for browsers for testing. ex: Firefox - Tidy, Web Developer. etc


3)How to apply the load on the web based application?
4)Tell me the procedure of stress testing of web based applicaton?

User Load Runner for these testing too.