2017 https://mirrors.ocf.berkeley.edu/parrot/misc/openbooks/progr...
2018 http://ebook.pldworld.com/_eBook/Reverse%20Engineering%20for...
In addition, some foreign languages still seem to be available:
French https://beginners.re/RE4B-FR.pdf
German https://beginners.re/RE4B-DE.pdf
Italian https://beginners.re/RE4B-IT.pdf
Japanese https://beginners.re/RE4B-JA.pdf
Polish https://beginners.re/RE4B-PL.pdf