Kent took another request on the AutoCAD Customization Forum and came up with an elegant solution. The request was how to find a point on an object a specified distance from the endpoint. If the object is a line or ray, you can draw a circle using the endpoint as the center of the circle, and then snap to the intersection of the line/ray and the circle. But what if you wanted to place something, or otherwise calculate a point, at a specified distance along an arc, or a polyline that bends, a spline, or partial ellipse? 

Kent’s solution works like a new Object Snap mode, which you can use like all the others, to find a location at a specified distance from either end of any open-ended object with linearity, at any time any command is asking for a location for any reason [point defining any linear/curvy object, either displacement point in Copy or Move, dimension definition point, insertion point for text/mtext/block/xref, base point for Scale/Rotate, etc.].
Load it up, and either type in (fe) [including the parentheses], or put that into a menu item/button somewhere and pick it.

It asks you to select an object closer to the end you want to measure from, and will only accept things that are open-ended with linearity.  It asks for a distance along it from that closer end to the location you want calculated.  You can either type the distance in or pick two points on-screen.  It shows you what the maximum distance is [the length of the object, except on a Ray], and if you ask for a distance greater than that, scolds you and asks again.  It remembers your specified distance and offers it as default on subsequent use, so you don't need to enter it again if you want to re-use the same distance.  It works in other-than-World Coordinate Systems.  It doesn't matter in which direction your selected object was drawn, nor whether you have any running Osnap modes on.