Niobium a.k.a. columbium is very safe for allergies (like titanium, its surface is automatically protected by an invisible but very resistant oxide layer). It has an interesting history, being one of the few metals (except the rare-earth metals) that have been discovered only after the beginning of the 19th century, in a mineral first found in USA.
However, it is not much softer than titanium or tungsten. Even so, it is quite frequently used for rings, piercings or medical implants with minimum health risks.
No metal suitable for contact with skin is as soft as silver and gold. For any ring made of another metal than these 2 you may need to go to a professional to cut it, if the ring cannot be taken out even with the help of some lubricant.
However, it is not much softer than titanium or tungsten. Even so, it is quite frequently used for rings, piercings or medical implants with minimum health risks.
No metal suitable for contact with skin is as soft as silver and gold. For any ring made of another metal than these 2 you may need to go to a professional to cut it, if the ring cannot be taken out even with the help of some lubricant.