I asked if there were any games where the PCs are not working together, and a few examples were suggested. Cold City is a great example of how a strong group structure can be used in a game. All the characters are part of a secret police force set up to deal with left-over Nazi occult weapons in post-war Berlin. You’ve got plot hooks and a reason to work together right there. Each PC is from a different country (a great roleplaying hook) and has a secret agenda (conflict! betrayal! plot complications!). There’s a Trust mechanic to bind it all together and bring it to the fore in every game session.