How to create an editable grid in dot net?

In the marketplace I can see a lot of partners are able to do that.

But how do I do that as a partner myself?

Can someone give me a head start or point me to the right direction?

I'm not creating it to sell at marketplace but my company is too stingy to buy any from the marketplace and they said, if other can do it, why can't we?

How do I start creating add on for Sage CRM?