I'm not sure if there is flanking in the sense that you must be properly positioned, but the game does allow for backstabs as well as penalties for defense when next to multiple opponents.
The game does also have blunt, sharp, etc weapons, as well as defenses against those types of attacks. Blunt weapons are more effective against the undead, where as blades are better on zombies. Armor can have bonuses to blunt, piercing, or slashing attacks.
Some blunt weapons do have a small chance of knocking opponents down. You have to examine the weapon tooltip, as it will have the chance listed whenever that happens to be the case. Some types of melee weapons have a higher critical hit chance, or more critical hit damage, cost less action points to use, etc.
There are stances for melee types that allow you to sacrifice accuracy for extra damage. There are also skills that will improve your ability to dodge or lower your defense penalties when flanked.
