Anyway, I am using Stella as an emulator and the dasm assembler on the command line, but the lecturer provides a link to this which is pretty amazing, a full online IDE, assembler, disassembler, debugger, range of emulators, all free:
https://8bitworkshop.com/v3.10.0/
Supports VCS2600 but also C64, MSX, Apple 2 and Z80 based computers including the Spectrum. Quite an impressive piece of web programming I must say!
You can code in assembler or C.
BTW the course I am following is on Udemy (I bought it for £15 but the sale is not quite as good today - £20 - btw udemy does sales every few months, so never buy a course at full price there!

https://www.udemy.com/course/programmin ... tari-2600/