Is there any website which is offering free real time tracking data of flights?
There are numerous web sites that provide flight tracking data, including radar and ADS-B. Most are free for personal use, but AFAIK all of them charge for commercial use. This makes sense since collecting and aggregating that data takes a lot of time, effort and equipment, and they have to recover those costs somehow. Still, using an existing service should be a lot less expensive than trying to set up your own redundant operation just for your own needs.

The sole exception is if you're trying to track ADS-B flights in the vicinity of your own facility, in which case you can easily set up a single ADS-B receiver there. But most folks want a (much) bigger picture, including non-ADS-B traffic, so please clarify the scope of your needs.