HoloFuel is a bit like Etherium gas. HoloFuel and HOT are designed differently and have different purposes. HoloFuel is designed to perform billions of daily microtransactions for hosting services and it works P2P. HoloFuel is Holo's native, asset-backed, mutual-credit currency. The cost for sending HoloFuel is a flat 1%, so it is ideal for micro or even small transactions.
Ethereum, Bitcoin, HoloToken (HOT, ERC20), and HoloFuel are cryptocurrencies.
p8: In the future the micro-transaction flows for hosting payments could also undergird a general purpose cryptocurrency payment system in a similar way that “gas” powers the Ethereum transaction engine.
p37: HoloFuel is credit to purchase hosting services on the Holo network. It works as a unit of account in Holo using value-stable double-entry accounting.
When it is released, you will be able to buy HoloFuel through the Reserve Account, third party exchanges, peer-to-peer, etc.