Having helped test NWShader this is what basically happened with the project AFAIK, and this kind of story is not unfamiliar to game communities nor even unique to the history of the NWN community, historically: A really talented and generous programmer took an interest in helping to update the graphics and spent an enormous amount of time to create, and re-create, and maybe even re-create again a program that would do just that. Each time he revised things, they got a little cooler and a lot more complex, each "bite" taken out of the problem, bigger. Until it looks like he finally took a bite so big, he lost interest in finishing chewing. And then he decided to take another bite out of another problem with another game, never to return and, except for the source code which he generously shared, the NWShader story ends there.
NWShader works by, among other things, intercepting OpenGL calls (the smallest individual packets of graphic data, like the hilt of a sword or a player's left forearm) and tweaking/adding/subtracting to/from them or running a filter of some sort over whole, completed frames to achieve some sort of graphic effect. Now that that definition is out of the way, there are a couple of different answers to the trailing question:
1) No. There isn't anything that does exactly what NWShader did.
2) Yes...sort of. A project like ReShade does full-frame post-processing but you need an OpenGL graphics card that supports something like at least OpenGL 4.4 (I believe) and the results are, IMO, not all that stunning. NWShader was, initially, written around how NWN 1 "did stuff" graphically and so with something like ReShade, there may be NWN-specific quirks/drawbacks.
3) Yes...if you want it badly enough to make it! While none of the other current OpenGL injectors/interceptors (such as those you might find on Google Code to gussy up older games like Quake, for instance) I believe it's possible to cobble together your own something-like-NWShader at least partly using an off the shelf bit of code like GLIntercept or, of course, editing the existing NWShader code, or at least what was available the last time it was checked into/distributed from SourceForge.
Sadly, 99.99% of all living human beings are only able to choose from the first two options. The last ones require very specialized skills and time. 
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