A simple programming language, like Amos. The sources are out there, so it should be not the biggest problem getting this on Aros.
I loved Amos as a programming language. It was the first and last one I did something useful with, I wrote a remote control program, using the serial port so I could control the Amiga in various ways elsewhere, be it on a Terminal emulation or a real Terminal (I had a Wyse)
Basically, an operating system needs a programming language that's accessible for everyone.
Next, but that's already covered, a decent Internet browser.