Modders have gained full "under the hood" access to the early 2000s legend.
Silent Storm
The source code has been released under a license that prohibits commercial use. Potential fines are stipulated. However, it is stated that it is fully open for "the game's community, education, and research."
Silent Storm was developed on an original 3D engine, primarily written in C++. The development team used Lua 4.0 for scripting events. You can explore how it all worked on GitHub here.
As for modifications, video and sound cannot be altered. They were created using proprietary technologies—Bink Video Technology and FMOD respectively.
Silent Storm
"We are thrilled that the 2003 Nival project has become open source," stated Sergey Orlovskiy, founder and CEO of the company. "Released more than two decades ago, the project is a cult classic of turn-based tactics, famous for its systematic approach and destructible environments."
Previously, the company also published the source code for another of its classics—the real-time strategy duology "Blitzkrieg."