All about Steins;Gate

Steins;Gate is the second and most popular title of the so-called Science Adventure series. This is a series of visual novels, anime, manga and more, all set in the same universe. There are currently four main titles: Chaos;Head, Steins;Gate Robotics;Notes and Chaos;Child.
These four stories take place in different times and are not directly related to each other, but some characters are mentioned or appear in the other stories. There's also the Committee of 300, which is supposedly the source of all evil that happens in this universe.
A full overview of all SciADV content can be found on the Science Adventure Database.

Chaos;Head, or Chäos;HEAd, is a science fiction and horror story, mostly about delusions, and is the first title of the SciADV series. The visual novel was released in 2008 in japanese and there is no official english translation, but a fan translation can be obtained via the internet. The anime adaption is considered not to be very good compared to the visual novel, but the visual novel itself is absolutely worth playing.
Chaos;Head Love Chu Chu! is a romantic comedy spin-off visual novel released in 2010, but there is no english translation yet.

Robotics;Notes is a science fiction story, mostly about building robots, and is the third title of the SciADV series. The visual novel was released in 2012 in Japanese. On March 23 2018 Spike Chunsoft announced they are intending to release a localization. Meanwhile, it is worth checking out the anime adaption which is quite good.

Chaos;Child, or ChäoS;Child, is the most recent and fourth title of the SciADV series. It's a sequel to Chaos;Head and set six years later. The visual novel was released in late 2014 in Japanese and in 2017 in English for PS4 and PS Vita. The anime aired at the start of 2017, but was not received very well.