I was looking for something like this for soooo long.

This one is going to go under many radars because of the formatting. The cover isn't interesting and the text is thick and weighty. But if you don't mind those very trivial things, inside you'll have many many items that could work in your campaign. Each item comes as a basic version. As an example, there is a greatsword called the Zweihänder of Agrimaugh. It starts as the "Corpseblade", an uncommon magic item. However, if your players find the "Dragonscale Shagreen" (a leather strip of dragon hide that wraps around the handle), it merges with the corpseblade, granting it additional powers. Finally, when a special condition is met (in this case, the blade cuts an adult dragon who is killed within the hour), it becomes a legendary artifact.

Every item is presented in this way. Base item, upgrades, final legendary form. All of it comes with lore that can be adapted for most settings and while the power levels of the items vary greatly, there's nothing here you wouldn't find in the Dungeon Master's Guide. A true hidden gem right here.