Nitroplus
Nitroplus, sometimes written as Nitro+, is a Japanese visual novel developer that has developed a number of visual novels, including eroge. They have been collaborating with TYPE-MOON (another developer) to create the light novel series, Fate/zero. They also have a branch of the company called Nitro+Chiral, which focuses on BL visual novels. Their works usually have dark themes such as reanimation of the dead and murder.
Mangaography

Katsugeki/Touken Ranbu
Nitroplus, Honami Tsuda, DMM GAMES

Steins;Gate
Nitroplus, Yomi Sarachi

Steins;Gate: Boukan no Rebellion
Nitroplus, Kenji Mizuta

Steins;Gate: Onshuu no Brownian Motion
Nitroplus, Takeshi Mizoguchi

Steins;Gate - Arc Light of the Point at Infinity
Shinichirou Nariie, 5pb., Nitroplus

Steins;Gate: Hiyoku Renri no Sweets Honey
Nitroplus, Tsutsui Taishi

Steins;Gate: Aishin Meizu no Babel
Shinichirou Nariie, Nitroplus

Steins;Gate: Shijou Saikyou no Slight Fever
5pb., Nitroplus, Yuzuka Morita, Tonene

Steins;Gate: Hiyoku Renri no Future Honey
Anri Sakano, Nitroplus

DRAMAtical Murder
Nitroplus, Torao Asada

Magi-Cu 4-koma - Steins;Gate - Sekaisen Hendouritsu x. 091015%
Masaru Oda, Huke, 5pb., Ryo Hazuki

Sweet Pool
Nitroplus, Mayu Kurumazaki

Azanael: The Case-Book of ENA
Hisato Murasaki, Nitroplus

Chaos Head
Nitroplus, Sumihei

Steins;Gate - Hiyoku Renri + Nyan² Crisis ☆
5pb., Nitroplus, nidoro

Togainu no Chi (Chayamachi Suguro)
Suguro Chayamachi, Nitroplus

Togainu no Chi (YAMAMOTO Kana)
Kana Yamamoto, Nitroplus

Blassreiter Genetic
Gonzo, Nitroplus, Shuu Hirose

Lamento - Beyond the Void -
Suguro Chayamachi, Nitroplus

Gekkou no Carnevale
Kazasa Sumita, Nitroplus