We will keep updating this throughout the workshop.
On Windows, the Notepad program that comes by default should work more or less okay. It doesn’t have tons of features, and you will have to make sure you save in the right place. But for beginners it is fine. One option with more features that is free is Notepad++ (https://notepad-plus-plus.org/)
On Mac, BBEdit (http://www.barebones.com/products/bbedit/) offers a free version that is quite full-featured.
Many other PTX (Mac, Windows, and Linux versions available) users enjoy Sublime Text (https://www.sublimetext.com) which is not free, but which has a package for PTX enjoyment (https://packagecontrol.io/packages/MBXTools) courtesy of Dave Rosoff of The College of Idaho. (Sublime Text is free to try.)
If you like the command line already, you can use nano, vim, or Emacs or their GUI equivalents. We won’t provide any instructions for those, other than to say that nano has hints at the bottom, so might be a bit more user-friendly. Mitch is an Emacs user, so if you want to use Emacs for PTX editing, feel free to ask him questions.
On Mac one can use the included “TextEdit” program. However, you will have to go through a little rigmarole to have it save things in “plain text” format. Go to “Format” and “Make Plain Text”; then you will have to make sure you save your files as “file.xml” as their filename, in the proper folder. Even then your mileage may vary with certain characters (notably quotes) saving incorrectly. View TextEdit as the editor of last resort.
If you want to explore the projects from which the sample pages in the introduction email were selected in greater depth, links to their main pages and print/PDF versions are collected here.
https://groups.google.com/forum/#!forum/pretext-support - the official support channel for PTX, at which you'll see many posts by users such as ourselves as well as the main developers
https://groups.google.com/forum/#!forum/pretext-announce - the source for official announcements about new features added to PTX (or the occasional syntax change)
http://mathbook.pugetsound.edu - the official website for PTX, with a fairly extensive gallery of existing projects at the bottom to get inspired
http://mathbook.pugetsound.edu/examples/sample-article/html/ - the sample article which shows off most of the capabilities of PTX in an entertaining, if non-exhaustive, way
http://aimath.org/textbooks/approved-textbooks/ - the American Institute of Mathematics list of open online texts that meet a certain minimal list of approval criteria for usefulness and broader adoption
http://open.umn.edu/opentextbooks/ - the University of Minnesota's open textbook library list, including many PTX books
https://openstax.org - another publisher of a variety of open access books, sponsored by Rice University
http://www.e-booksdirectory.com - a directory of various freely downloadable ebooks