3D Movie Maker (commonly shortened to 3DMM) is a children's computer program developed by Microsoft Home's Microsoft Kids subsidiary in 1995. Using the program, users can make simple films by placing 3D characters and props into pre-rendered environments/backgrounds, as well as adding actions, sound effects, music, text, speech and special effects. Movies are then saved in the .3mm file format.
The biggest fan-community of 3D Movie Maker, 3Dmm Studio, still works, even though it wasn't updated since 2006. Visit it to find useful tools and archive of user-created movies. Or you can use our forums and its dedicated 3DMM Studio thread.
In May 2022, Microsoft published original source code of the program, which can be obtained on GitHub or Archive.org
3D Movie Maker has an addon available: Nickelodeon 3D Movie Maker, don't miss it!