SMBX 1.3:
https://wohlsoft.ru/docs/SMBX_Old/info.html

SMBX-38A:
https://smbx38a.wohlsoft.ru/

SMBX2:
https://codehaus.moe

Moondust Project (formerly known as PGE):
https://wohlsoft.ru/projects/Moondust/

TheXTech (modern, extended and cross-platform port of SMBX 1.3):
https://wohlsoft.ru/projects/TheXTech/