Known alternative to DMX512 & RDM
Well there is ACN, specifically S-ACN which was supposed to replace DMX but is kind of complicated. 

Then there is Art-Net which is something Artistic License came up with that basically encapsulated DMX in UDP, popular because it is simple (Unlike ACN!) and lets you stuff a lot of DMX down a ethernet link (512 channels starts looking a bit thin when pixel mapping a big display). 

That plus DMX deals with the current common ones in entertainment lighting, there are about a dozen other more of less historical ones (PMX, D54, Martin were seen in the UK, and I think Colourtran had something in the US market, then there were the two 0->10V standards (Strand used 0-> -10V, everyone else 0 -> +10V), one wire per channel.

Outside the entertainment game there are some commonly used for architectural work: DALI and DSI, plus some propitiatory ones common in offices and the like.