Expansions typically refers to two of the official additions Armageddon's Blade and Shadow of Death, which both continue the story that was started in Heroes of Might and Magic III: Restoration of Erathia. The original game was first released on February 28, 1999, and was followed by its first expansion Armageddon's Blade, seven months later on September 30, 1999. The second and final official expansion, Shadow of Death, was first released on March 31, 2000. Both expansions can be installed independently of one another and require the original game to be installed first.
On October 2, 2000, Heroes of Might and Magic III: Complete was released. It allows installation of both the original and its expansions in a single package.
On September 27, 2000, The 3DO Company began releasing extra single player campaigns as chapters in a series. All of the chapters can now be purchased as Heroes Chronicles. It is a beginner's introduction to the Heroes of Might and Magic series.
See links for other noteworthy Heroes of Might and Magic III projects and resources.