This article details works not officially released by Type-Moon. This is not an all-inclusive list, but rather a reference page for doujin works that have some direct connection to an official Type-Moon work. Please do not add any entries without first confirming some form of connection.
There are many doujinWP works relating to Type-Moon. This article deals with those directy referenced by official works.
Gugalanna - The Bull of Heaven
Gugalanna - The Bull of Heaven is a doujin by PFALZ detailing the battle between Gugalanna, and Gilgamesh and Enkidu after Ishtar releases it upon them. A slightly re-designed version of this Gugalanna was officially utilized by Type-Moon in 2017 with Gugalanna's inclusion in Fate/Grand Order as part of the seasonal event Dead Heat Summer Race!.
SWORD DANCERS is a series created by Himura Kiseki. It follows Archerko, a version of Illyasviel von Einzbern who has become a Counter Guardian with similar abilities to Archer. In reference to this work, Himura drew Illyasviel in an end card for episode 6 of the first season of the Fate/kaleid liner PRISMA☆ILLYA anime adaptation.