Never used it so far, but recently came across the NEO keyboard layout [1]. Unfortunately the website is in German only, but just looking at the interactive graphic should give you sufficient information how it looks like. The only German word you need to know to understand the graphic is „Ebene“, which means layer. What I find particularly interesting is „Ebene 3“, or „layer 3“ and the corresponding repurposing of the capslock key. Personally I definitely intend to try the NEO layout soon.
[1] https://neo-layout.org/