I love the ARP 2600 synthesizer. The mighty Macbeth M5 was a new incarnation (there were differences I know). Software-wise the closest you can get is the TimewARP 2600 from Way Out Ware. To play and hear one in person is to want one.
“The ARP 2600 is a semi-modular analog subtractive audio synthesizer, designed by Alan R. Pearlman (and Dennis Colin), and manufactured by his company, ARP Instruments, Inc. Unlike other modular systems of the time, which required modules to be purchased individually and wired by the user, the 2600 was semi-modular with a fixed selection of basic synthesizer components internally pre-wired. The 2600 was thus ideal for musicians new to synthesis due to its ability to be operated either with or without patchcords, and was, upon its initial release, heavily marketed to high schools, universities, and other educational facilities.” – Wikipedia
photo credit: Ethan Hein