GalliumOS makes nightly iso builds. These are functionally identical to Beta isos, but they contain newer packages and experimental changes to the base OS. DO NOT use GalliumOS Nightlies in production or machines that you rely on for day to day life. You shouldn't use GalliumOS Nightlies at all unless someone on the support/troubleshooting team tells you to, you want to get involved and help test new features, and/or you're totally prepared for everything to go horribly wrong at any moment.
GalliumOS Nightlies are built every day by our build server @ ci.galliumos.org. If you're looking for the most recent nightly, check out the last successful build. If you're looking for a different nightly, check out the GalliumOS-Nightly project. We use Jenkins to manage our build system.