Actually IGNIS is a child chain of ARDOR, which is the network... oh wait: Ardor is going to be the network when NEXT disappears, which will be shortly after the NEXT network is forked to become ARDOR...

In reality it is quite simple: It is all the same thing, iterations of the same thing. Implementations of some new improvements, scalability and features, but the exact same thing... they simply call it different things to be able to sell it as different things. And guess what? It is working like magic ... for them, the "team".

Keep an eye of the dumping of NXT already in progress (but nothing compared to what's coming as it goes obsolete). Fascinating.