'Elf friends' (Nisse venner) is the Danish version of 'Secret Santa'. In Denmark it's mostly arranged by middle school teachers for their students though, and less commonly by adult groups. Just like Secret Santa the game is about giving gifts to the person you were assigned to, without them knowing who you are. Then at the end of the month everybody has to guess, and if someone is not guessed by their gift-receiver he or she wins the honor of being good at being sneaky...
Maybe contrarily to 'Secret Santa' the game of 'Nisse venner' is very focused on distracting/misguiding your subject so they wont guess who you are. Also you're expected to not only give gifts but also mess with them a bit. This is the best part of the game; getting creative with duct tape or snow-spray is extremely fun.