Note: The original official binaries are only provided via Codeberg for use by other developers, not any app stores. Please mind the security notice and lack of warranty.
You can get the Horse64 development kit on the code sharing platform “Codeberg”, here's the desktop default for Windows PCs:
SDK
for MS Windows (x64)
Download
(From Codeberg)
For other devices, check here:
Note: If you're adventurous and curious, raw source is here.
Horse64 and Moose64 are free and open-source with BSD-2-Clause or Apache 2 terms, click for details (the only exception being the official branding images, which you can swap out). Also, third-party things have their own licensing.
Go here.