Freshly loaded contextbeta an hour ago.
Retrieved simplefonts from the ConTeXt site.
Unpacked the zip and put the t-simplefonts .lua and .tex files inside  
the directory where all my context (user) input files reside.
Read the (somewhat terse) documentation.
Ran contextbeta on:
\usemodule[simplefonts]
\setmainfont[schoolbook][schola]
\setsansfont[helvetica][heros]
\setmonofont[courier][cursor]
\starttext
Hello world!
\stoptext

Result in the log:
system          : module simplefonts not found
! Undefined control sequence.
<recently read> \setmainfont

l.3 \setmainfont
                 [schoolbook][schola]

Now what? Why are my files in the same directory found and simplefonts  
is not?

Hans van der Meer