There are lots of things I miss. Datatypes is definitively one of them. AREXX ports everywhere (I hate the language, but you don't need the language to make use of AREXX ports; Dbus is like what you get if you take AREXX and give it to a committee; the beauty of AREXX was the sheer simplicity that made it so trivial to add support for it to "everything" to the extent that many tools built their central message loop around checking for AREXX commands and built their application around dispatching AREXX like commands between different parts of the app).

Assigns is another one (for the non-Amiga aware that stumble on this, on the Amiga, I'd refer to my files with "Home:", but unlike on a Unix/Linux, Home: is not an environment variable that needs to be interpreted like $HOME or something that needs to be expanded like "~" - it is recognised by the OS as a valid filesystem path, assigned at runtime; similarly, instead of having a $PATH that needs to be interpreted, all my binaries would be accessible via "C:" for "command" - "C:" is an assign made up of multiple actual directories, one of which would typically be Sys:C, where Sys: is the System volume, and Sys: itself is an assign pointing to whatever drive you booted; Assigns are like dynamic symlinks with multiple targets, or like $PATH's interpreted by the OS)