Related, there's a suggestion in the StarlingX community at the
moment about the possibility of incorporating SAP's Elektra UI
( https://github.com/sapcc/elektra ) as an alternative to Horizon:

http://lists.starlingx.io/pipermail/starlingx-discuss/2020-September/009659.html

Looks like it's a mix of Apache and MIT/Expat (Apache-compatible)
licensed Javascript and Ruby/Rails. Given there's not really any
Ruby in OpenStack proper (except for Ruby-based configuration
management and maybe SDKs), I expect that may not be a great
starting point for a next-generation Horizon, but it could still
serve as a source of some inspiration. Also this highlights an
interest from some of the StarlingX contributors in Horizon
replacements, so maybe they'd be willing to contribute... or at
least help with requirements gathering.
--
Jeremy Stanley