Jun and Jot is a "terminology" that was used initialy by Jumkey and are in terms of conseption the same thing. A buildroot that performs all the actions after an upgrade and then uses kexec to boot dsm using the patched kernel and the patched ramdisk.
Jumkey analyzed the buildroot concept and introduced that on his own repo and then it was adapted by TCRP and later by ARPL.
TCRP friend came later than ARPL cause that was the time for TCRP to adjust to new technics. TCRP friend has its own repo and its own wiki.
https://github.com/pocopico/tcrpfriend/wiki
Of course both TCRP and ARPL are based on the same initial concepts but with some enhancements. ARPL currently, as it was designed from scratch having all these technics in mind, will adjust easier in a future upgrade. Some TCRP friend features are uniq like static IPs, Hidden boot messages, loader backup etc. But still missing some features, like eudev. Eudev was adopted partially but will break in case of an update by TCRP friend as this is not yet implemented.
Also Fabio further assisted with numerous issues like. dtbpatch, kernel patch, LKM development, new patch development etc.
I'm further developing the TCRP loader and will adopt all these in a future release.