Tibia is a classic 2D game that was one of the earliest MMOS. Released back in 1997, the game features sprite graphics, a quest and job system, and a variety of monsters. There are many servers to choose from, with a mix of PvE and PvP-specific ones available.
Tibia is still being updated and balanced from time to time, and despite being an old game, still attracts thousands of players. The game is free to download and play, but a premium subscription is available that unlocks several more areas, cuts XP loss after death, allows use of the transport system and allows player owned homes, among other benefits.