Mike Udin Fast Spline Connector is a plugin for Cinema 4D that connects segments of a single spline. Starting from un-joined splines, you select two points and connect them quickly without manual measuring.
The workflow centers on a distance tolerance. Select two points and press the Get button to set the correct tolerance automatically, then refine it with minimum and maximum values to find points more accurately. If the current tolerance is not enough, increase the value a little. Join mode creates a new segment between the connected points, while Weld mode merges two spline points into a single point that lies at the mid-point of the welded points.
An automatic extrude option is included, and you can customize interpolation, chamfer, and segment length options for the connected points. It supports Cinema 4D versions from R17 through 2023.