The Conclave Add-on for Crusader Kings II has 10 achievements.
Have all members of your council be Loyalists.
Enforce peace for 6 or more vassals.
Successfully intervene in a youth's development to force one of your own traits onto them.
As a ruler have a council that is not content.
Win a war using Mercenaries.
Create a mercenary band and have them bring in money for you.
Have someone owe you a Favor
Sit on the council and have every other council member as well as the ruler owing you a favor.
Have at least one child with each of the five level four education traits.
As a vassal use a favor to change a law.