You do have to pay licensing fees though, if you're selling a commercial application that requires MUI. That's why there's so few commercial releases using MUI (Drawstudio, Ibrowse...?) and lots of 'Shareware' releases.
When I bought IBrowse 20 (!) years ago (heh) it came on two floppies (another heh). On the first disk was IBrowse 1.0 and on second shareware version of MUI 3.0 without a license key. I dont know if they paid something to Stuntzi to distribute shareware MUI but I doubt it (*). Bigger problem was that you had to ship MUI thus increasing costs and complicating install. Impractical in the world of 880K floppies.
Another thing is that it is easier to adopt old program to use ClassAct than MUI due to their different philosophy. However...
* Or maybe they did (see Kamelito's link).
Agreed. Not to mention that AmigaOS has its very own GUI system which could use some attention aswell.
It should be blown away and replaced with new class set.
RA/CA classes work surprisingly well and are quite feature rich for its time. But when developer is using CA he has to write tons of glue code to get simple things working together. It is also suffering from lack of class hierarchy and inconsistent notification system.
tl;dr CA/RA issues are not so much in the user side but its developer interface need streamlining.
Jens and Thore are pushing MUI, because it benefits their cross-plattform approach (YAM...). For AmigaOS users (and, to a lesser extent, MorphOS and AROS people) this simply means that the amount of applications not properly adopted to OS4 (i.e. using Ringhio and application.library, OS4's support for translating codepages into the native ISO-8859 etc.) is going to increase.
I think it is moot point.
The cross platform approach does not prevent using vendor specific extensions. YAM can use Ringhio and OS4 codepage translations when compiled to OS4 target, and it could use MagicBeacon and charsets.library on MorphOS, for example.
And there is multiplatform codesets.library that takes an advantage of some/all OS4 and MorphOS codepage translations.
It's like 1995/1996 all over again: no leadership, no strategy, no money - the obvious result is bedroom coders doing whatever they feel like doing.
Remember when computing was fun ;^)