Fast X-ray Transients (FXTs) are minute-to-hours long flashes of X-rays, first discovered serendipitously in X-ray satellite data (mainly Chandra and XMM-Newton). They are proven to be caused by energetic extra-galactic phenomena. Currently, Einstein Probe is revolutionizing the field by discovering many FXTs and, crucially, by their low-latency announcement thereof. These extra-galactic FXTs are ubiquitous: their density rate is several hundred per year per Mpc^3. FXTs have been proposed to arise from double neutron star mergers, tidal disruption events involving an intermediate-mass black hole and a white dwarf, and from off-axis or sub-luminous gamma-ray bursts. Brief extra-galactic FXTs also arise in supernova shock breakouts. Contemporaneous multi-wavelength detections possible only in the current Einstein Probe era show that FXTs originate from more than 1 progenitor. I will discuss the most recent findings and provide some (potential) science questions to be answered using FXT observations.