RCX is the earliest robot in Mindstorms. And it is the first robot in Lego that can be programmed to control Motors and get data from sesnors. The software for programming RCX is Robolab. And Robolab 2.9.4 is able to program NXT. Unlike other programming softwares below, Robolab is not free. You have to get it from Lego Store. Then you need to download the 2.9.4C patch. instructions are provided in the video below.
Robolab 2.9.4C Patch(Windows)
You can also download it from here
Robolab 2.9.4C Patch(Windows)
You can also download it from here