There are a total of 135 collectibles in Remember Me.
40 Mnesist Memories, 25 SAT Patches, 15 Focus Boosts, 55 Scaramechs.
Finding all of them will max out your health, give you bonux XP, unlock special move slots and earn you 4 trophies or achievements.
These collectibles are scattered across all 8 story episodes. The prologue does not have any collectibles. In Episode select you can see how many collectibles of each type you have found in every episode. The Journal and Status Menu show your total progress.