In the current version of Heroes By Trade I have a system that controls how people use magical items called Vessels. Characters can attune to Vessels to gain access to their abilities and benefits. This Attunement process is different from Vessel to Vessel - an executioner's axe might require you to chop off the heads of people guilty of treason, a jewel might require you to wear it in your necklace for a year while signing a song to it every day, and a roc's feather might require you to save birds from danger. In this way characters have quests and stories that unfold as they get access to greater abilities.
How many Vessels you can Attune to is regulated by the Presence stat. Presence functions much like Charisma does in DnD but I like the name better because this stat also determines how powerful your influence on the world is, and thus how many Vessels you can control. This all worked well, as far as I am concerned.
A couple days ago In The Hat emailed me to suggest that this system might be used to allow people to have familiars by using their Attunement slots on the familiar instead of a Vessel. Wizards having magical pets or rangers having animals that follow them around is a constant trope in fantasy, so it seems quite reasonable to allow this in some fashion. I haven't so far though because as a class function pets are a real problem. They never end up balanced in combat and always end up being broken one way or another. Sometimes they just die to AOE effects and then are useless, other times they are invincible and end up being able to block hallways and doors in ways that just shouldn't be. In extreme cases they end up more powerful than other characters.
However, if a pet or familiar comes into the game using this system it isn't going to be a powerful combatant. It might provide combat bonuses to the character, but mostly it would act as a scout, have magical abilities, give access to skill bonuses, or something like that. It could be really interesting and it would be easy to figure out how good the pet should be by looking at the guidelines for Vessel power. I really like this idea.
I think the idea can be further expanded though. Rather than Attunements being about Vessels with an exception for familiars I think they should be much more broad. For example, if there is a battlefield where a horrible magical battle took place and the battlefield is magical and/or haunted, a character could Attune themselves to that very place. This could grant them substantial powers that are related to the battlefield and which mostly apply only if the character is there. Think of a druid in a sacred grove, a paladin in a holy chapel where a desperate defence against undead took place, or a warlock defending their tower. In these places these characters often manifest special abilities and are much stronger than they would be otherwise.
I wouldn't necessarily expect a lot of players to choose this option because players usually move around a lot. However, having that be a thing would make it possible for the GM to build opponents that truly are terrifyingly dangerous in their lair and not have it wreck the game world otherwise.
Probably the best way to approach it would be to have players Attuned to places gain a small benefit that goes with them, perhaps half of the normal benefit of a Vessel in power, but have a massive benefit worth double what a Vessel normally is that only applies when in the area that the character is Attuned to. This way it doesn't feel worthless under most circumstances but it is truly amazing when that character is in their home base.
This also opens up the possibility of having characters Attune to other things. Rather than pitch Attunement as being about controlling Vessels I could simply say that it gives you power over the world and make controlling Vessels, places with special magic, and familiars as three examples. That gives the GM freedom to decide what other possibilities might exist and a framework for figuring out how powerful those possibilities should be.
I find this especially appealing because it makes Presence awesome. I love the idea of people having this gravitas, this potency, that others can detect and having that be part of the world. For all of Naked Man's criticism of Presence I don't think even he could resist stacking a lot of it if he could see all kinds of really cool stuff you can do with it.
Possibly I should also change the way I do Attunements. Right now they are set up so that you get one Attunement at 3 Presence, 2 Attunements at 7 Presence, 3 Attunements at 11 Presence, and 4 Attunements at 15 Presence. However, instead I could just assign each Vessel, familiar, or magical place a value and say that it takes that much Presence to Attune to it. All current Vessels would convert to taking 4 Presence points to control, but I could easily create new ones that are extremely powerful and require a lot of Presence, or relatively trivial ones that take less.
So many grand new ideas to play with!