Uh, thanks. I saw a rs97 on Aliexpress and the sellers claimed it had opendingux, but probabily they were taliking about the retrofw.
To be honest, only the software developers who work on the things really understand the difference. Everyone else uses "OpenDingux" as shorthand for "custom firmware". If you see "OpenDingux" advertised pre-installed on an RS-97 or related unit (e.g. LDK, RG-300, etc.), it's probably RetroFW.
Note that RetroFW also goes by the name "Tony System" in a lot of AliExpress ads. Long story. Suffice it to say Tony Jih was a main developer on RetroFW.
There were two other custom firmwares: 97Next and Useless. The latter of which was developed and maintained for a while by the previous poster, GBB. If I understand correctly the former was developed by Stuart-Fu & Jutley. (I'm sure I'm leaving tons of people out who made all this stuff work.)
RetroFW learned from the previous two and added a lot of enhancements. So at this point there's no real reason to run anything else. The OS is extremely well tuned to the needs of JZ4760(B) devices. Newer devices ship with the RetroFW OS instead of the stock Dingoo OS. And if you want to upgrade or heavily customize your device, many models make the internal SD Card easily accessible under the battery.