MiniSphere

minisphere is a modern replacement for the aging Sphere 1.5 engine. It is not a fork of the original engine's codebase; it is a completely new implementation written from the ground up in C, based on Allegro and Duktape, and includes support for modern features such as OpenGL shaders and CommonJS modules. The vast majority of the Sphere 1.5 JavaScript API is also available for use in minisphere, with only a few functions missing from the implementation. A complete implementation of the Sphere 1.5 map engine is also included and built in.

The minisphere engine is available in both x86 (32-bit) and x64 (64-bit) variants, the latter of which is recommended as it typically provides better performance. The engine is tiny, requiring only 1.7 MB for the 64-bit engine and the official Windows build is completely self-contained in a single executable. As it is coded in C, it is also very portable and has been successfully compiled on both Linux and OS X platforms.

As of this writing (June 10, 2015), there is not yet an official site on the Web for minisphere, but the engine is available for download and discussion on the Spherical forums here. The current official release is minisphere 1.2.3.