It is the continuation of the Sandboxie Application.
The Plus version has all the configuration settings included while some settings are missing from the legacy version.
I suggest to use the version from sandboxie-plus.com website since it only includes the stable builds, the github page builds iterate between stable and testing builds. The versioning of the file is in the filename. ex. Sandboxie-Plus-x64-v0.9.8.4.exe