Not yet investigated keyd.
I still use good old .Xmodmap tricks on Linux, and AutoHotKey on Windows. Plus some VIA macros directly on my programmable keyboard.
And I [plan to] investigate kanata (https://github.com/jtroo/kanata)
Kanata is good. I use it to have some consistent keyboard configuration between Linux and Windows.
One nice feature it has over AutoHotKey[^1] is that it can use Interception (a keyboard filter driver) to handle keys earlier, which lets it work in more situations (e.g across RDP sessions). Interception itself though does have a bug where if you keep adding/removing devices it will stop working until you restart.
1: I've seen an Interception module for AHK, but it's not built in like Kanata's
I've tried about ten billion different tools on linux and can confirm that kanata is better than everything else mentioned in this thread and a lot more. It's not the right tool for global hotkeys, so it's not going to completely replace something like AHK or wkhd, but it's basically the closest thing to QMK functionality for a laptop or non-programmable keyboard.
