Can you register a .com domain with namecoin? Namecoin is a generic name-value store, so I'm wondering if its possible to register .com domains in namecoin. The answer here seems to suggest you can register any domain you want How do I register a .bit domain name with Namecoin?
Namecoin was the first fork from Bitcoin, and is a blockchain based peer-to-peer network which maintains a decentral ledger of registered names.

It is the convention, that when you register a Namecoin name starting with d/ that appropriate DNS resolution software would translate this information to a .bit address. E.g. d/myself would be resolved to myself.bit.
On the other hand, the responsibility for managing regular top-level domains (TLD) is assigned by the Internet Corporation for Assigned Names and Numbers (ICANN) to specific organizations, with which a regular user can then register a domain directly or through intermediaries.  

The ".bit" domain used by Namecoin didn't exist in the Domain Name System (DNS) before. As far as I am aware, there are no conventions for established top-level domains. That would be especially problematic in the case, when the two resources managing the same namespace would end up with conflicting information: 
It would be somewhat detrimental to the user experience if domains were to resolve to different pages depending on whether you used the Namecoin extension or not.

Another example of Namecoin usage is the application OneName, which resolves names starting with u/ to point to Bitcoin addresses of their users.