ENVMATH.COM does math with DOS environment variables. What good is that, you say?
Well, for starters, you can control looping within a batch file- try that with plain DOS! Since ENVMATH allows incrementing (+1) and decrementing (-1), it is easy to run a loop, say, 10 times- or 26,153 times! ENVMATH also can compare two variables, so you can keep looping until a target is reached, like 0, or maybe your age. Used in conjunction with ENVSAVE- a bit of freeware bundled with it- you can set up batch files to count how many times the machine is booted, or a certain program is run. You can use it to generate numeric parameters to pass to other programs. Remember, any Windows program can be started from a batch file, too!
Note: Unfortunately, ENVMATH will not work on Windows NT systems due to system security restrictions (they are not really DOS).
Tools used in the creation of ENVMATH:
NASM the Netwide Assembler