Prey (2006)

Prey is a FPS released in 2006, developed by Human Head Studios under a contract with 3D Realms and published by 2K Games. The game runs on a modified version of the id Tech 4 engine (Doom 3 engine), incorporating unique features such as portals and gravity manipulation to enhance the player's exploration experience.

You play as Domasi "Tommy" Tawodi, a Cherokee who, along with his girlfriend and grandfather, is abducted by an alien ship known as The Sphere. This ship consumes both living and non-living material from Earth to sustain itself. Thanks to his Cherokee heritage, Tommy possesses the ability to send his spirit out of his body, allowing him to traverse the environment freely and even return to life after death—giving him a distinct advantage as he fights to escape the Sphere's clutches.

One of the key gameplay elements is the use of portals, which allow players to instantly travel between different areas. These portals can be seen through, shot through, and even crossed in both directions, but unlike the later games Portal, they cannot be created by the player without modifications, and they remain fixed in the game world. Another significant feature is the variable gravity mechanic. Certain areas of the game enable the player to walk along paths that defy gravity, allowing them to stay upright regardless of their orientation. If the player falls or jumps off these paths, normal gravity will take effect. Additionally, small planetoids within The Sphere exhibit their own gravitational fields, allowing for exploration of their surfaces in full 360-degree motion.