Well yes, I thought about proxy servers but what I need it's not that, I need a web server to connect to a program in an user computer, only when a request to the web server is made. Thus, I need the program in the user computer to be available all the time. What a proxy server does is:

- Receive a request from user.
- Retrieve the requested data.
- Send it to the user.

What I need is:

- A user loads a web page.
- The web server requests some data from another user's computer.
- The web server shows the data to the first user in a web page.