RPG Maker VX Ace (RPGM) provides the ability to create 2D Role Playing Games, with a turn based battle system with random encounters.
Specifically, the player cannot see the enemies while walking around an environment and will encounter them randomly. When an enemy is encountered, a battle start animation is played on the screen and the player is taken to the battle. The battle is then unfolded by each character (the player's party members and the enemy's troop members) taking turns performing actions. An example of such a battle can be seen here.
In an action battle system (or Real Time Battle), the player can move freely around the map, can see the enemies and choose which enemies to fight or not. Also, they can attack and cast spells freely whenever they want, while also get attacked by other enemies without provocation.