I was able today to install RedbeanPHP via Composer.
I was able to install Redbean using a simple "require": {"gabordemooij/redbean": "3.*"} entry in my composer.json file.
The only 'gotcha' seems to be, that the 'R' class is not the default 'facade' - so the instructions in the Redbean manual won't work. To overcome that, at the top of my php file, right after including the composer autoloader, I added:
use RedBean_Facade as R;
That seemed to do the trick, but I don't know whether this is the 'recommended' way of using Redbean with composer. It would be wonderful if Gabor could add an entry in the manual about this, to help people like me who are 'easily confused'! ;-)
It's awesome that Redbean keeps evolving, and adapting to the latest and greatest technologies! Thank you, Gabor! :-)