For April, Harry's picks include the following:
Draw Rectangle from Midpoint — Walt Bedinger — This routine allows you to draw a rectangle in AutoCAD starting at the midpoint, or center point (as opposed to one of the corners).
Rename Every Block — Dennis Jehan — Add a prefix to every block in your current AutoCAD drawing.
Viewport Zoom — Robert L. Zipprich — You might be thinking that applying a zoom XP scale to a viewport is already possible in AutoCAD, but Robert's routine works in older versions of the software, and also includes multiple scale units sorted by type, including Architectural, Engineering, Decimal, and Metric.
Create Stirrups — Raymond Rizkallah — Create stirrups for structure beams in millimeter drawing units.
Dynamic Layer Isolate — Lee McDonnell — This LISP routine works just like AutoCAD's built-in LayIso command, expect that as you hover over an entity, the layer is isolated in preview mode so that you can see the result before making your final choice.