"In September of 2016, a talented programmer released his own cooked update to a major company’s legacy operating system, purely because it needed to be done. A raft of new features, wrap-in programs, and bugfixes were included in this release, which I stress was done as a hobby project.
The project is understatement itself, simply called Prodos 2.4. It updates ProDOS, the last version of which, 2.0.3, was released in 1993.
You can download it, or boot it in an emulator on the webpage, here.
As an update unto itself, this item is a wonder – compatibility has been repaired for the entire Apple II line, from the first Apple II through to the Apple IIgs, as well as cases of various versions of 6502 CPUs (like the 65C02) or cases where newer cards have been installed in the Apple IIs for USB-connected/emulated drives. Important utilities related to disk transfer, disk inspection, and program selection have joined the image. The footprint is smaller, and it runs faster than its predecessor (a wonder in any case of OS upgrades).
The entire list of improvements, additions and fixes is on the Internet Archive page I put up [ https://archive.org/details/ProDOS_2_4