After SunTour went into a long slow decline, it transmuted into SR SUNTOUR and moved from Japan to Taiwan. And throughout the 1990s the derailleur range gradually decayed into a mish-mash of low-end, sub-Shimano steel and plastic.
But the arrival of the new millenium seems to have re-energised SR SUNTOUR, which suddenly produced a whole set of aspirational, innovative and freaky looking derailleurs. These featured straight cable runs, and many had a unique ability to be compatible with both Shimano and SRAM levers. They achieved this seemingly impossible feat by cunningly having two possible ways you could run the cable on the one derailleur.
I believe that this interesting item is a SR SUNTOUR NCX (600 SGX), however I have also seen it called SR SUNTOUR XCR (650 SGX), although I believe that is a different design. The '600 series' number may indicate that one knuckle is aluminium and the other is plastic. It featured:
I think this is my earliest version of this basic derailleur design, before the dual-compatiblity feature was added.