Comment by bbanyc

The most significant contribution that DEC BASIC made was the REPL-like "immediate mode" that lets you execute individual statements without having to RUN the whole program. It was copied by both Microsoft and almost every other BASIC implementation since. Being able to fiddle around with "PRINT 2+2" is so fundamental to the BASIC experience that it surprised me to learn that Kemeny & Kurtz didn't come up with it, DEC did. (It came from DEC's earlier language FOCAL, which had an "English-like" syntax and doesn't resemble BASIC in any other way, and probably ultimately from LISP.)