The Charlemagne Add-on for Crusader Kings II has 13 achievements.
Play as a Tribal Ruler and Reform to Feudalism
Play a game all the way through from 769 to 1453
Found the Holy Roman Empire in a game starting in 769
Rule as Emperor with the Reformed Zun Faith
As a Christian non-Saxon, completely conquer Saxony in a game starting in 769
As an Anglo-Saxon or Saxon ruler, be king of both Saxony and England
Be King of Frisia and hold the Atlantic coast from Léon in Brittany to Jylland
Become Emperor of Francia as Carloman, brother of Charlemagne
Hold any Emperor or King title as a Lombard after 1300
Have a capital province with Norse culture and Muslim religion
Be simultaneously at war with the Aztecs and the Mongols
Divorce a Lombard Princess as a Christian
Play as a Tribal Ruler and Reform to Merchant Republic