Weapons of Legacy
Weapons of Legacy refers to both a splatbook for Dungeons & Dragons 3rd Edition and the concept it was created to promote and support. In a nutshell, Weapons of Legacy was an attempt to offer an alternative to the "Christmas Tree/MagicMart" style of D&D, where characters would have to increasingly replace their magical weapons (or other items, but mostly weapons) with newer and more powerful versions as they gained levels in order to stay combat viable. The WoL system attempted to offer an approach more readily seen in other media, including videogames, where characters could have unique magical weapons that grew in power alongside their wielder through the performance of various magical rituals to provide them with the requisite boosts.
Unfortunately, the published weapons are quite lacking in quality and aren't worth what you give up. Some argue that the actual underlining system is fine and can be used to build good options, but that depends on learning a subsystem to chuck out half of it. One particular knock against WoL is that the Ancestral Relic feat from Book of Exalted Deeds did what the book tried to do but better within a single page. The feat allowed characters to sacrifice treasure at full value (instead of selling it for half) to add its value to their favorite item.