XTRABYTES™ was never an ICO, but rather a community-driven project.
XTRABYTES followed the failed Bitmox ICO. In early 2017, Bitmox investors lost money when the project's developers decided to abandon their project. In order to create a real community for the Bitmox victims, XTRABYTES’ lead developer Borzalom stepped in to resurrect the project, repair the source code, and rebuild the node network.
Thus XTRABYTES never raised any money for its development. Borzalom rather forked the old Bitmox chain and premined all the new XBY coins to the C-CEX exchange, where XBY first started. This was done so that C-CEX could credit all the existing accounts that owned the old Bitmox coins with the new "official" XBY tokens, and then the XTRABYTES chain continued forward, leaving the old Bitmox chain dead in its tracks, which also eliminated the old duplicate accounts with the Bitmox coins. The original Bitmox investors thus received XBY tokens instead of their now worthless Bitmox coins, and most of them decided to put their XBY up for sale on C-CEX.
In order to further the development of the project, XFUEL was later created. XFUEL is an internal development token on the XTRABYTES blockchain. As such, it serves as a way to both fund the XTRABYTES project and encourage further participation within the project. As a monetary incentive, XFUEL serves both to encourage further investment in XTRABYTES and pay participants for the hard work and time they put into it. You can learn more about XFUEL here.