After you finish the game, three more short mission forming an epilogue will appear on the map. The last of them can be found in Boston, where you will learn of the so called Pivot points which you have to find in order to unlock cheats in the game options. How to do it?
Start off by making sure you're connected to the Internet, turn on the map and check the "Animus Synching" tab. There you will find information on the available pivots and a map with the locations of the others.
Two first pivot points will be marked on the map of Boston. The line which goes through them divides the city into two halves and the green colour marks the area where the next artifact is hidden. If you click on an existing point you will be able to delete it and pressing the Connor icon will place a third point where you're standing.
By manipulating the lines, you can widen the area. Using the two first points, you can tell in which half the artifact is. Place a third pivot point and you will form a triangle. If it's green, it means that the artifact is within its field. Otherwise, remove one of the points, run to a different location and place the points there. It's easiest to search for artifacts in cities, as you can use fast travel which speeds things up considerably.
The first pivot can always be found in Boston on the roof of a building, but others are placed by other players in various places.
To find where the next pivot has been hidden, head to the "Pivots Info" menu. You can move through it with the right analog stick. There you will also find the time when further pivots become unlocked.
Pivots are needed in order to unlock cheats in the game menu. Below you will find a full list:
2. Unlimited ammunition.
2. Ability to change seasons.
3. Ability to change weather.
4. Lightning strikes after each kill.
5. Ability to change time of day.
6. No firearms reload time.
7. Enemies can be assassinated even during an open conflict.
8. Ability to call in recruits without any limits.
9. Enemies ignore you completely.