One of the biggest appeals to the series XCOM is just how easy it is to get attached to a character. It's always fun to see that nobody rookie you recruited pull off some amazing feat time and again and rise through the ranks of your army to become the biggest and baddest alien killer on the block. Modder RealityMachina had the brilliant idea of taking this attachment one step further and created a mod for the game that allows for a, "squadmate score" system that allows teammates that work well together to develop bonds that give buffs to the squadmates that trust each other, similar to Fire Emblem's Bond Support system.
Characters gain affection with one another by doing things like carrying a wounded soldier to safety, stabilizing a fallen ally, or healing a friend's wounds. After a while, the teammates gain benefits when they work together which allow for increases to damage, accuracy and other attributes.
However, since XCOM has never been a series to just hand you everything, there are also some risks involved with this process. There are penalties included should a friend fall -- such as the surviving member gaining shaken status, which will reduce their willpower stat for a period of time.
Updates like these are what make games like XCOM 2 so great. It will be interesting to see what other ideas the community has in store for us. If we're lucky, maybe we'll see a sequel to the famous mod for the first game The Long War, which even the developer's have described as, "a 20-hour tutorial for Long War."