This mod makes followers (both humanoid and otherwise) essential (meaning that they cannot die) while they are following you.
It also makes the bows and arrows that (humanoid) followers wield levelled, so that they can infinitely shoot arrows with more powerful bows.
These scale with the follower's level, and start being the follower's bow at the level that the equivalent enchanted bow would become available. All bows are weightless and have the same speed as the default hunting bow.
Note, however that this means that followers with level caps lower than the level that the equivalent enchanted bow becomes available will be restricted to bows that would appear at their level.
Version 1.1.0 adds magic to all followers, and gives them 100 extra magicka and a fortified healing rate while they are following you.
Version 1.2.0 adds many more spells to followers, adds to the amount of magicka they gain by being a follower and adds edited versions of a few spells that are more magicka efficient., including a two handed spell that replenishes their magicka supplies. Edited Adrianne from Whiterun to be a follower with a unique class, to act as an example. Version 1.2.1 allows followers to interact with their environment, somewhat akin to Serana from Dawnguard. Sneaking will override this, to prevent them from becoming an annoyance.
Version 1.3.0 adds to followers the ability to heal you.