On February 26th, developer Matty (aka @Mosk_i) has officially released Pyboot along side of SuccessionDown.
Pyboot, being a Ra1nsn0w alternative for tethered booting iOS11-13 that allows for things such as custom boot logos.
SuccessionDown, on the other hand is a fork of Succession by developer SamIsAninja which is used for fully restoring your iDevice without having to restore your device. But, SuccessionDown is used purely for on-device tethered downgrades.
This comes recently after many in the jailbreak community discovered that tethered downgrading via Succession is possible.