What's the difference between ETH and ETHW? Is it a fork? And will there be two currencies after the Merge will take place?
It is a fork that not yet has happened. (when ETH is POS, ETH POW will start) (around 15 september)
Ethereum POW and ETHW is the same thing. The sourcecode has removed the difficulty bomb, removed POS code, removed some of the stablecoin adresses/ tornado cash adresses/ and hacked accounts. Implemented replay protection to make sure the new blockchain can co-exist with the original Ethereum. The work is stil in process, and more will be added.