Splines creation

Below you will find C4D plugins for generation of spline primitives or spline based objects.
Some are more like C4D spline primitives (eg. ArrowMaker, ArchSpline), some are more like C4D generators (Kurulumun, Umami).
Some need an input object (e.g. Vector Pro needs a picture., Spline Wrapper and object around which it can wrap around)

Vector Pro Better vectorizer transforms bitmaps pictures or any shader into splines or flat, extruded surface ($)	ArrowMaker Generate parametric spline in form of an arrow which can be customized (free)	ArchSpline Spline-primitive producing different types of arcs with parameters allowing to adjusted arch shapes (free)	3D Meier Various math related plugins allowing to generate function defined surfaces, splines, cylinders intersections etc... (free)	Lorenz Attractor procedural spline generator creating a spline in form of... Lorentz Attractor - obviously ($)	Kurulumun Generates curly parametric splines that twist randomly by 90°. It is also a generator - can create surface on its own. (free)	Umami Generates parametric random splines (looking lie noodle like). It is also a generator - can create surface on its own. (free)
Primitive Sketch draw and size spline primitives directly on objects surface. It can do the same for object primitives and offers scattering (video) (free)	DragSplines : creates and sizes spline primitives with mouse, also on objects surface ($) TIP : PrimitiveSketch also allows to create and size spline primitives on objects and does it better than DragSplines.	NoLoopSpline : spline for transmission drives, track, that don't create inverted loops (use Reverse on circle spline to invert a +loop) (download) (free)	Spline Wrapper : wraps spiral splines around objects ($)	ct-maze-trace ♥: generates splines that wander along mesh edges creating a pattern similar to labyrinth corridors (free)	splineCAGE generate splines from edges, can offset spline in normal direction and use Edge Selection Tags (R17 OK, R18 crash) (free)	EdgeSweep : Generator which creates SweepNurbs out of Edge-Selection Tags. I put it here, among splines, because what it does is almost exactely the same as splineCAGE (R18 OK) (free)
Net Creator generates splines connecting components or objects.Vertex maps can be used to drive propagation of connections. (free)	Uber Tracer generates splines connecting components or objects. It extends the feature set of the MoGraph Tracer. Can create nice plexus effects (free/$)	pCONNECTOR : generates spline segments between Source objects (incl Clones, Particles, Splines) and PointSelection Tags. A lot of unique settings (free)	Spline Connector : generates splines to connect objects and mograph instances, but can't connect components (free)	RayConnector : connects only Thinking Particles with splines (maximum distance, maximum number of connections) etc... (free)	SuperTracer : spline generator, that can track state of input object over time. It supports following modes "Chain", "Net", "Web" ($)	PolyEdge Spline : Generates a live spline from continuous edge selection on a mesh (no separate edges, no forking) - the mesh is hidden (free)
Topowire : generator creating multiple pending lines between objects. (hair, spline, sweep) ($)	HoRope : generates setup for animating dynamic ropes (video) (free)

Splines modification

CV-Splines (To Objects) : A set of commands and generators for splines : Single click commands for spline Extrude, Lathe, Loft, & Sweep. 2 Genertors for interactive outline/offsets spline and chamfer, Helpful for non-destrucive spline modeling. 2 Generators for creation of hanging wires and connections between cloned objects.
MANUAL VIDEO ($)

CV-Catenary generator ♥ makes splines hanging down. Great for hanging wires, ropes, and cables.	CV-CrossStitch generates splines between objects in a hierarchy (siblings, children, cousins), or between MoGraph Clones and manually specified connection points	CV-Chamfer generator creates a chamfered version of the spline	Outline generator creates an outline or offset of the original spline	CV-Render Splines makes the selected splines renderable as hair (automatically ads hair tags to multiple objects, render effect, special tags. Works with deformed splines)
CV-Sweep Splines command adds a C4D Sweep generator for selected splins. It adds a n-side spline for section (for easy control of segments). Use the Scale to adjust the pipe radius by eye.	CV-Extrude Splines command adds in one click a C4D Extrude generator to multiple splines. Generators are conformed to splines axis.	CV-Lathe Splines Creates C4D Lathe generators for selected splines, and position them for each spline (using various criteria eg. spline bounding box, lathe axis X, Y, Z)	CV-Convert to Loft : select splines in space, and puts them into C4D Loft generator.

Patch Modeling

Coons Mesh : generator that creates coons patches from 4 splines (free)

SplinePatch : patch modeling to create smooth, curved surfaces from intersecting splines which is especially suited for cars, clothing... (review) ($)

SPLURF : provides patch modeling in C4D with spline surfaces ($)

NitroModel : makes 3D object from hand drawn outlines (similar, but not exactely patch modeling) workflow focused on creation of characters ($)

Surfacer : spline patcher to generate surfaces based on 4 splines (XPresso rig) (free)

Cross Nurbs : create polygonal plane by crossing two linear splines ($)

Discussion about efficiency of Patch modeling tools for C4D

Scripts :

With first two I couldn't get any useful refults - those are py scripts, so maybe they can help you if you are learnig py programming in C4D :
reduce_splines : intelligently reduces the number of points in a closed or open spline (free)
expand_splines : takes an open spline (a line) and turns it into a closed spline (polygon) of desired thickness along the original line (free)
output_spline_points : outputs spline points and name (can help to export to code lines) (free)