That would depend on what type of meat you are tenderizing and how it is being cooked. Something as simple as cutting the meat across the grain can make a tough cut of meat seem more tender.
For items like pork, veal, or chicken schnitzel a meat mallet works fine.
For items like a cube steak, a mechanical cuber or a knitter, is much less work than pounding with a textured cube meat mallet.
There is also a jaccard, however i am not a fan of these because they can push surface bacteria into the center of the meat. So if I am not using a marinade with an acidic content, I don't use them.
If you are talking about additives to tenderize the meat:
Marinades contain an acid and some salt to help denature the proteins, making the final product slightly more tender; however due to the molecular structure, these only work on the surface (about an 1/8th of an inch), the inner meat remains tough and flavorless.
There are also dry brines and wet brines that will denature the proteins and add flavor while making the meat more tender. These can penetrate deep into the meat when given the proper allotment of time.
Lastly, you have enzymes available like powdered bromelain (from pineapple) that are tenderizers. I haven't used these so i have no input.
Finally, depending upon what you are trying to make, try a better cut of meat or possibly even a better grade.
.