If someone can summarize for thoses who still have not been invited (as me despite my several PM ...)
Like niklasmato said there is no ICO for xfuel. There will be an exchange called X-Change that will be powered by the XBY network where xFuel will be paired with XBY. You will be able to use xFuel to fill up to 30% of L2 & L3 nodes in place of XBY. The price of xFuel will be determined by the market. Right now the only way to gain xFuel is to earn it.