I have implemented with 3 friends a gamified system at my work (development company) which builds an fantasy rpg game over scrum project methodology. Generally, the tasks are the missions, each player is represented by a character. They earn XPs for completing tasks and they advance to the next levels which gives them badges, titles and (this is in planning phase) new privileges (e.g. priority in choosing tasks).
Since the very beginning we try to do everything to avoid rivalisation between players because it would ruin the project if the players started to compete. There are no explicit leaderboards, we also plan to give bonuses for helping other players.
I have a feeling that this is still not enough to really encourage cooperation. I would like to ask You for any ideas that come to Your mind that would help.