The main tool in CURVEmachine that makes this possible, is the Blendulate tool, which allows you to create curve radii/arcs (or non-circular blends), change existing ones or merge them back to a single point again.

Features:
add a single-point poly curve at the cursor's location to quickly start extruding a curve
create, edit or undo curve radii or non-circular blends
slide a curve point along its previous or next segment
merge to the last selected point or to the center of the selection, including across two splines
shuffle the gap of a spline to another location
adjust curve thickness, extrusion and resolution, and toggle spline cyclicity
interpolate curve point thickness and tilt
connect two splines