This ring is simply called the “Hayte Necromancer Ring” because this ring was in possession of an undead necromancer hanging out in the The Cider Spider, and the ring itself has a tiny blood red dagger design on it which is the holy symbol of the god Hayte.
This ring entered the campaign when the aforementioned necromancer encountered the wizard Jeorge at The Cider Spider. Jeorge had asked about raising the dead and the necromancer all too eagerly gave him this ring immediately.
The instructions to use it are to put it on your middle finger, stand over some bones, and cast any second level spell using the ring as a spellcasting focus. This takes the second level spell slot's power, and instead of casting the selected spell the ring channels the magical energy into the bones of the dead, raising them as a vaguely controllable skeleton.