The Soul Memory system in Dark Souls 2. It matches people together for PVP and Co-op based on the total number of souls that character has collected over the course of the game. The soul memory tiers are actually rather large when one looks at the numbers, depending on the form of PVP/Co-op the player can reach players a certain number of tiers above and below their own, and there are items in game that can expand your range. For those unfamiliar with the Dark Souls series, souls are dropped by enemies and double as experience and currency to be used both for leveling and acquiring items and equipment.
I really like this system. It allows me to continue leveling my character without risk of reaching a deadzone for multiplayer, as happened in previous games which matched players together based on their character level. This lead to a really aggravating "community level cap" and if you went any noticeable amount above this, then the online portions of the game were essentially cut off entirely. No co-op, PVP was rare, and one of the best parts of the game ceased to exist, forcing you to plan your character from the beginning of the game with with very little room for experimentation lest you put too many points into the wrong stat and end up too far above the cap. All it did was encourage min/maxing from the get go, and allowed devious players to avoid leveling, acquire VERY powerful elemental weapons that don't scale based on your stats but had VERY high base damage, and then invade and repeatedly kill newer players.
People say Soul Memory leads to build homogenization for PVP, but honestly nothing more than what I saw in Dark Souls 1, and allowing the player to continue leveling allows them to experiment with new things and try some truly crazy combinations of gear and spells. That coupled with limited weapon/armor/spell slots means that people will gravitate towards equipment that suits their play-style. Also, I can still get summoned at higher levels to help people, and still am able to find assistance for tricky fights myself.