Experimental seed viewer / NBT editor / Data Pack IDE for Minecraft JE 1.14
This is about 3-5x faster than AMIDST (the leading competitive seed-finder) and shows twice the resolution.
I used the reverse engineered and optimized algorithms from cubiomes to generate most of the terrain. I manually reverse-engineered certain terrain passes.
I had to reverse some of the structure finding methods myself as well, particularly the newer ones.
In addition, there is a from-scratch NBT viewer written.