The current version is v2021.03.21a [PDF] (single-column format [PDF], change log), AKA second edition.
The default double-column format is easiest on both the trees and the eyes in paperback book form. The single-column format works well on large-format ebook readers. Medium-format ebook readers reportedly do well on single-column PDFs that have been run through PDF-cropping tools, a number of which can be found by doing a web search for “pdf crop”. All attempts to generate epub formats for small-format ebook readers have produced horrible results, but if you know of something that works, please don't keep it a secret!
If you would like a dead-tree copy, please feel free to use any of a number of internet-accessible printing services, or you can find dead-tree copies of the first edition here. If you would like a fancy dead-tree copy, here is some shiny new artwork for front and back covers, courtesy of Melissa Broussard. The older cover art is still available for those who prefer the classic look (front and back).
Contributions are welcome, and to that end, a public git tree may be found at:
This git tree also provides an up-to-date version for those who are too impatient to wait for the next release. There is an email list (email@example.com, subscribe here) for feedback, patches, review, and discussions.
Older versions are available as well:
The second edition is available here. The first edition and older versions are available here.
New releases should appear three to four times a year, give or take. This work is covered by the terms of the Creative Commons Attribution-Share Alike 3.0 United States license.