Thes are templates for pocket-size books.  They are for MS Publisher, made with the "side fold card" template (which simplifies the process), but they could be made with any desktop publisher.

 

    Download a template and go to the box with "1."  The numbers indicate the pages of the final document: erase them.  Paste in the text of your choice, and it will flow through the frames until the end.  Adjust font, spacing, etc.  Print on both sides of the sheet, fold, bind, and slit the edges.

 

    The 16-page octavo is for one 8.5" x 11" sheet, and "32pp_together" is for two sheets, one nested in the middle of the other for binding.  The only time-consuming part is extending a document.  You will have to add pages corresponding to a third or fourth sheet, and although you can copy-paste the text boxes, I don't know how to replicate the links between boxes except by repeating the sequence of links as in the first sheet or two.  "32pp_sequential" does that for two sheets.  Or just create a separate document for every signature.  There is more than one way to fold up a sheet, but the way it's done here results in several of the of the first eight pages corresponding to the quarto pages of the side-fold-card template, which makes things less confusing.  Possible tweaks could be using A- or B-series paper (so the aspect ratio doesn't change with folding) and making templates for open-source programs.  I've tried it with Scribus, but it took a while and the result wasn't satisfactory.