For the system, it's a ruleslite game based off of version 2.0 of Ben Milton's game, Maze Rats. The most notable feature of the original game was the idea that spells would consist of keywords, and you would spend HP to cast magic through the spell according to its name. As an example, a PC wielding the spell "Pursuing Beast" can use it to create a hawk or an owl to spy on his enemies, make a giant monster of his design to kill his foes, or even use the magic to augment the tracking abilities of his hounds. The only limits are the breadth implied by the name of the spell and the number of hitpoints the PC is willing to spend to create more powerful or long-lasting effects.
This idea was so much fun that I expanded upon it. Instead of making spells tattoos (and therefore non-transferable and not able to be found as loot), I made it so that they were encased in physical items that can be bought, sold, and stolen. I also made a bunch of guidelines to help players and GM alike decide the cost of various magics so that there didn't have to be so much "GM may I" going on.
Among other things I added included a set of status conditions, many different weapons with slightly different mechanics that I hope are true to real life, and subsystems for called shots and grappling and counterspelling and reactions. The reaction rules I am particularly proud of, because combat is a lot more interesting and fluid when you can do things like duck for cover, block, protect an ally, counter a spell, or flee from or intercept or pursue a foe, all during your foe's turn. It's pretty neat and encourages players to pay attention.
So suffice to say, this system is kind of my baby, and I love it dearly.
For the campaign itself, we actually just finished it last week, after 50 sessions. I'm tempted to write out an outline, but it'll likely be over a thousand words. I guess I'll give it a shot if no one minds a wall of text.