System666 is a fast, easy math language. Currently available for DOS (works under Windows). Check it out.
ZenonSA is a no-frills surface area and volume finder. Currently available for DOS (works under Windows, does work in Windows 2000).
ZenonSAR packs the same power as ZenonSA but does I/O streams. Currently available for DOS (will work in a Windows DOS prompt, though not through an icon).
Some of these may never leave the ground, but some will. Check these often!