How can I post on Hive blockchain without registering for an account?

You can login to this account @forwarddao using the Posting Key: 5K4qnzQxbiMWKcFG3woEHq8bfNBwDEmp8zEKLiqhUQZ37FDLa1m

But you cannot receive any Author Rewards from the post (if any) unless you have an existing Hive account to set as Beneficiary. In fact, the whole point of creating a Hive account is to claim Hive-based Rewards for your interactions (posting, curation, and etc) on Hive blockchain. Or else, you may set other's accounts as Beneficiaries and they will be able to receive Author Rewards from the post.

This is the open posting key expiriment: Here is the key to the kingdom: 5K4qnzQxbiMWKcFG3woEHq8bfNBwDEmp8zEKLiqhUQZ37FDLa1m