A free app for Windows, by XF-Alien.

The game is called Half-Life: Delta Mod. The main character is an engineer named Nick Farell. He is an employee of the Black Mesa Research Facility, where an experiment is being conducted that could send aliens to Earth. Unfortunately, the outcome is not what was expected. The result is a series of waves of alien creatures called Xen.

How to play

The game is single-player, so you will be the only player. You need to use your device to navigate through the world and interact with objects. The game is divided into four chapters, called maps. You can start playing in chapter one, and if you finish the first map, you will be able to move to chapter two.