Sekai Project is an American video game publisher best known for licensing and translating Japanese visual novels into English, but they have also published manga and other non-visual novel video games.

Originated in 2007 as a fan translation group translating the visual novel School Days, they later partnered with publisher JAST USA, turning their fan translation into the official English version of the game.

In 2014, Sekai Project began publishing games on Steam; their first title being World End Economica episode.01. They also used the crowdfunding platform Kickstarter to fund many of their projects.

Since Steam does not typically allow adult games to be sold on their platform, Sekai Project releases their adult titles through their partner company Denpasoft.

[Edited from Wikipedia]