Mobile internet tethering without paying anything extra definitely seems like a blessing, but carriers are against this following which they have started charging extra for internet accessed on laptops through smartphone as a hotspot.
Recently a very prominent developer and hacker Koushik Dutta - also known as Koush has created a non-market app for Android, which permits users to use their smartphones as internet hotspot and that too without a penny extra except the cost of data usage on the smartphone.
Being in alpha state, the app might have some bugs in its current form. The app is nearly undetectable by carriers, reported Slash Gear.
The present version of the app is temporary and will expire on January 7th. Thus, it is better to wait for the final version which will be permanent but, most probably it will not be released on the Android Market. The first release of the app is available for free download through Koush's Google+ page.
There is no need to root the Android device to be able to use it and it allows desktops, laptops to use internet connection of the Smartphone to access the web.