The following images were created as I played around with trails in Houdini.
The trails are curves that are advected through custom vector fields. Some are basic vector fields using curl noise. Others are controlled by a new HDA I made for manipulating vector fields with curves and mesh surfaces.
I created a few different super fast curve shaders based on this forum post and from this entagma video. I also added to some of these shaders to get some custom results for random colours on curves, colour over length and for adding gradients across curves.