d3-tricontour
Create contours from non-gridded data with meandering triangles.
flubber
Best-guess methods for smoothly interpolating and animating between shapes.
cdt2d
Constrained Delaunay Triangulation in 2D
tess2
GLU tesselator ported to Javascript, performs polygon boolean operations and triangulation
libtess
Polygon tesselation library, ported from SGI's GLU implementation.