TheSans Monospace has been derived from TheSans, the sans serif part of Luc(as)'s Thesis family. This new variation started as a kind turn to Thomas Merz, probably the most expertised PostScript programmer in the world. In his book "The PostScript and PDF Bible" TheMono is being used for all PostScript code. The idea is simple, give all characters equal widths. However, it turned out to be a very interesting and time consuming job. It took another 9 months to grow to its final state.
The MonoSpace appears to function very well for correspondence. A written letter in ThesisMono immediately has a personal communicative touch, and doesn't look like a detouched "print type".
A considerable amount of time has been invested in achieving an optimal screen display. For often used sizes (9, 10, 11, 12 and 14 point) the bitmaps have been hand-pixeled. (These work on mac only.) Because of extensive hand editing of hint-instructions, TheSans Mono is optimally readable in other sizes as well as on PCs with Adobe Type Manager. A delta hinted TrueType package for the office environment is on its way.
TheSans Mono is used by O'Reilly for printing code in most of its tech publications.