A newish app with a very good rating (4.7). As usual, no ads or IAP.
MobilCAD 2d Pro is an easy to use 2D CAD program with all the basic functions of a CAD program. The data elements line, circle, arc, dimension, text and symbols can be used to construct 2d drawings quickly and easily. These can be saved as a PDF or DXF file and distributed via Google Drive. MobilCAD 2d Pro is the ideal CAD program for students, and CAD beginners. With the Pro version you can select and edit any number of drawing elements. For a quick edit Griphandles are available for all elements. The dimensioning tool has been extended with radial, arc and angular dimension. For all dimension types there is the possibility of text overwriting. Snap is tangential and perpendicular possible and the polyline can contain any number of holes.
Would that be a worthy upgrade for OzBargain forum posts needing MS Paint diagrams?