Plants vs. Zombies software version 3.1 is a tower defense game where players use various plants to defend their homes from a zombie invasion. The game features 50 levels, each with different challenges and objectives, and includes mini-games and puzzles. Players can unlock new plants and special abilities as they progress through the game, and can also play in multiplayer mode. The software has colorful graphics and a quirky sense of humor, making it a popular choice for casual gamers.