There are metallic cappers, that come in a straight line " stick " formation. Those will hold about 20 caps at a time. Tedd Cash makes two cappers, one shaped in an oval that will hold a full 100 caps. The other looks like a tear drop of a comma, and will also hold 100 caps. Then there are the hand made cappers made of leather. A thick piece of leather is punched around the edge with hole large enough to encompass a cap, with a slit from the hole to the edge to aid in releasing the cap once it is placed on the nipple. For safety, a second piece of leather is place( sewn) on top of the first one so that if a cap were to fire when being put on the nipple the thumb(or finger) would be protected from the blast.
I am sure that there are other shapes and types of cappers made, or that have been made, but these are the common ones seen over the past 40 years. The choice of cappers often depends on the type of gun and period of history you are portraying, if that kind of thing matters to you. I had a stick capper when I first began with BP guns, as that was what was available. When Tedd Cash products came out with his oval shaped capper, I bought one, and still have it 30 years later. The only percussion gun I now have is a DB shotgun. I sold the stick capper shortly after selling my percussion rifle, and converting a new gun to Flintlock.