If you use them that is, which tools are absolutely necessary to have? I've been on the Gravimetric site and the NL Development Center site and both have quite alot of tools. I'm not sure which ones I really need.
Once you get used to them, no. but at first they can seem quite confusing, especially the H:sak. Experiment with them a bit, soon enough you'll find out what each of the functions does. If you're good at math and stuff, you should find it should be quite easy.
The key is the math ... you have to remember the formulas of the equation for the previous element to ensure your transitions are proper, but once you get the hang of that it becomes quite easy.
I don't use any tools to make my track but i use tools to make my track better. The de-pumper and the smoother in the construction kit works a treat. Sadly it's not available to buy anymore which is a real shame.
You only really need to be good at math if you want to create formulas. The most advanced math required to use pre-existing ones is simple addition and counting.
The one tool that you simply cannot be without is the NL track packager. If you don't have it already, you really need it.
AHG is a must for Intamins, B&M's, and GCII woodies. It will save you tons of time and make heartlining coasters really easy. I also reccomend getting a copy of buster's track smoother, which is a nice way to get rid of some of the little bumps in the track. Finally, you'll want an object creator. I reccommend Tia's 'object creator', because it is so easy, but Anim8or is also a great tool if you are willing to take the time to learn it. I'll admit that Elementary is also a good tool, even though I don't use it personally.
So:
-NL Track Packager
-Automatic Heartline Generator
-buster's "Track Smoother"
-"Object Creator" or "Anim8or"
-"Elementary" (depending on if you want to design coasters using math or manual labor.)
I have pretty much all of then, regardless of whether I use them or not. They hardly take up any space, and I can just pull it out if I want to figure out how to us it. I no longer use OC due to lack of flexibility and optimization, except when I want to nab a few textures from there for work on anim8or. Maybe in a rare case I might need OC for something simple, then I import it into anim8or, merge points together, and do some more work on it.