Illustrator's shape primitive tools (ellipse, rectangle, polygon, etc.) are, well, pretty primitive, even compared to other mainstream general purpose vector drawing programs, which are not really anything to write home about either.

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Why is it that so-called "professional illustration" programs are so tyrannically fixated on the vertical and horizontal axes? Don't programmers know that real-world illustrators think in terms of the axes and thrust lines and construction guides of their drawing, not the mere edges of the page?

Link to example image JET_Ellipse.jsx
Illustrator's Ellipse tool only lets you numerically specify an ellipse in terms of height and width. Technical illustrators need to be able to define an ellipse in terms of size (major diameter) and "tilt angle," as ellipse drafting templates are labeled. This script prompts the user for those two values and draws the ellipse at the center of the artboard. Default values are set to 1" and 36.25, values appropriate for a 1" ellipse in an isometric projection.

To Use: Run the script. Key values in the two prompts. The ellipse is drawn at the center of the Artboard.

Link to example image JET_PolygonBySide.jsx
Illustrator's Polygon Tool only lets you numerically specify a polygon in terms of height and width. This script allows you to specify an equilateral polygon by the length of one side.

To Use: Run the script. Key values in the two prompts. The polygon is drawn at the center of the Artboard.

Link to example image JET_RightTriangle.jsx
You can easily draw a right triangle of a given rise/run by first drawing a rectangle and then removing one of its anchorPoints. This script allows you to specify a triangle in terms of the length and angle of the hypoteneuse.

To Use: Run the script. Key values in the two prompts. The triangle is drawn at the origin of the Artboard.