First Person Melee appears in many games, with ranging levels of importance. For example, a game a game like Quake features a melee weapon as a last resort weapon; in the Halo series only uses a single attack while always holding a weapon, usually used as a last resort. In games like Zeno Clash or Breakdown, however, it takes a more prominent role, featuring combo systems and dodge maneuvers.
This applies to games where we can use a ranged weapon as a melee weapon, like buttstroking, pistol whipping and using bayonets or other attached melee weapons on the firearm, these are a few options that exits in many Shooters today.
This applies to games that always have you equipped, but no matter what weapons the player is using, there will always be the same alternate weapon to strike with. The most common example is the boot from Duke Nukem 3D or the knife in the Call of Duty series.
The most uncommon type, this only applies to games that rely more heavily on the First Person Melee concept. Games that use this system typically downplay the use of firearms and have controls to accommodate the change in movement, such as a lock-on system and fighting mechanics more commonly found in more traditional fighting games. An early example was The Super Spy and the most recent example would be Zeno Clash.