XL is Viking Hordes Mod,
Its similar to Superhigh or Supermod (The Blind Kings project) with new factions, provinces, buildings, and units but unlike Supermod, in XL the Glorious achievments still work . BKB's mod is more expansive and experimental, with lots more new units and buildings but there are still a few glitches to iron out. Both are excellant (if not essential) game enhancements. There are several versions of Supermod, Superearly, SuperHigh and Supermod plus Superlate the add on for Supermod. The last two are the most rescent which include everything to date and are self installers.