Which manages the domain registrants itself, bills them and there complete system is automated ... ???

eNom - PDQ is one of several (GoDaddy etc.)
one advantage of eNom's solution is you can now have it in English & 3 other
languages. Downside is only US dollars.

You can use eNom.com's PDQ system ($99 yearly license fee), which is a full domain name sales website that is ready to use with about 5 minutes of configuration. (ie: Just sign up, set your pricing, and it works.)

eNom also offers a free "registry rocket" system, which is much simpler and also allows you to sell domains quickly and easily.

(Most of our resellers use the registry rocket, because it is free and it works well for basic domain name sales.)