Spline Bridge
Spline Bridge links polygons to create a bridging effect. As you can see the Numeric panel doesn't offer many options, but operation is simple. Select one or more contiguous polygons on each object you wish to bridge and start the tool. If you select multiple polygons and they are not contiguous - they don't touch, the tool will not work. By default Divisions is set to 1, but often you'll want to increase the number of divisions to better bridge gaps. Handles are available to direct the bridging and the First Twist and Second Twist options are there in case the bridging becomes twisted (this happens sometimes when polygon normals are not conducive to bridging and the point order has to be revised).
Only a single group of one or more contiguous polygons on separate objects can be bridged. If non-contiguous polygons are selected on either separate object, Spline Bridge will start, but no bridging will be done.
The cursor keys can be used as shortcuts for this tool. Up and Down will increase and decrease Divisions, while Left and Right will do the same with Twists. When the cursor is nearer one end than the other, that is the end that will be twisted. Otherwise, the First Twist will be changed.