Anarchy Online. I got into making over powered low level characters and helping random teams through the popular low level dungeons.
Most gear had a stat requirement instead of a level requirement, so the more effort and arcane shit you could put up with, the stronger you could get your character. Laddering, equipping pillows that buffed strength, that allowed you to put in better stat boosting implants, that allowed you to put on better stat buffing armour, that allowed you to equip better strength buffing pillows, that allowed you to put in better implants etc etc until you couldn't keep track of everything anymore. Loved that shit.