AmigaBASIC! Used it on my A1000 for a year, then bought a compiler that could build executables out of AmigaBASIC code. Wrote my own terminal program with a zillion bells and whistles. This was after learning TRS-80 Level II BASIC in the late 1970s.
Man I forgot all about that compiler that made executable basic code. I had that too. I miss those days! Your terminal would have had a heavy lift to beat JRComm but I bet it was fun to write.