Suitable for printing as a zine-style booklet
The primary differences from BX are ascending AC, consolidation of some fiddly bits like ability score adjustments into standardized modifiers, and trimming of some things I see as extraneous like prime requisite XP adjustments, extensive rules for water and air travel, and encumbrance by tracking the weight of every item (two new Encumbrance options are added).
Special thanks to Gavin for both taking on the endeavor of creating B/X Essentials, and for conferring with me on attribution. It should also be noted that Gavin is further refining, compiling, and re-branding B/X Essentials to Old School Essentials, and the new editions will include Ascending AC.
As a side note, this (along with the original version of Principia Apocrypha) also serves as an example of how one can wring decent-looking, printable zine-booklets out of Google Docs. I might eventually write up a guide and templates for what I've learned.
I encourage you to comment below, rather than elsewhere.
Long live the Blogosphere!