New self-defense tools come out nearly every day. Some are must-haves and others are more novelty or entertainment-type items.
For example, having a small kubotan on your keyring can be very helpful, but the cat-looking brass knuckles on your keyring look a lot more like a novelty item than a self-defense tool.
I’m pleading the fifth on this one. 
I don’t think it’s necessarily self defense but the Gerber shard is a nice little EDC tool. I recommend those to people who want something small and can be used as a pry bar, screwdriver, bottle opener and other various things
Besides a sidearm, I always carry a Hoffner 3.5" folder. It has so many things going for it, the circular indentations for immediate access and 100% sure grip, it acts as a tactical pen (without the pen), and it opens as fast as a switchblade … but has no springs so it is legal in Pittsburgh PA, where I live. I love Hoffner folders!