Pretty much all Allwinner based SoCs used in common SBCs have FOSS firmware. Some older Rochcip SoCs also do, but you have to be careful there (the most open/fu

Pretty much all Allwinner based SoCs used in common SBCs have FOSS firmware. Some older Rochcip SoCs also do, but you have to be careful there (the most open/fully featured is RK3399). That covers a huge amount of SBCs out there. Some even have multiple alternatives for FOSS firmware. If anything RPi seems like an outlier. Out of 9 different SBCs models I have at home only Rpi2b and Quartz64-A have proprietary firmware.