Having been basically a bit-pusher (computer programmer) since the early '70s, Dave has written hundreds, if not thousands, of utilities and special-purpose software packages over the decades, and is available for custom software development. Here are a few utilities, plus an HTML Quick Reference that Dave wrote in the mid-nineties, which has been used by people worldwide who have been learning HTML.

• Calendar Functions: Show a month or year calendar for any month or year within a huge range of years, calculate days between dates, calculate offset from a date, calculate the date of Easter for a given year, etc. This particular version of the calendar utilities was written in PHP, although previous versions have been in Perl and JavaScript.
• Financial Functions: Calculate simple or compound interest, print an amortization table, and more.
• HTML Quick Reference: A reference manual for (virtually) all the tags in HTML, each tag having a Syntax section, a Discussion section, and an Examples section.