I have a web application with I want to use for registered users to be able to use it.
I am looking for a wordpress plugin that can restrict specific users to use web application.
So bascally a user to user signup web service.
Is there anything specific to that in wordpress?
You may use one of these plugins
http://wordpress.org/extend/plugins/s2member/
http://wordpress.org/extend/plugins/paid-memberships-pro/
Users could pay for access to your application or you can create user group and allow access only for it. If these plugins are not usefull for you may find what you need there