Calm Balm is a potion in C3/DS that comes with the Hardman Norn pack.
It is used to calm down the Hardman Norns when they feel particularly aggressive and begin to take their anger out on their surroundings. Leaving a few around the ship can train your Hardman Norns to drink it when angry.
In addition to decreasing anger, it increases sleepiness and tiredness, so it can be used as a sleep aid.
MNB has created a Calm Balm Vendor which you can install in your world for ease of dispensing Calm Balm. Steelfoot created a Giant Calm Balm which also dispenses calm balms. Alex created a Calm Balm Vendor which is a smart vendor.
Kezune made a three-part study on the safety and use of calm balm as a sleep aid, which can be read at her blog, Designer Genes.