free freebsd book by greg 'grog' lehey.
"Ruby Grundlagen โ PDF zum Buch 'RapidWeb Development mit Ruby on Rails'"
linux kernel internals for enthusiasts (yr. 1999 / kernel 2.0.33)
open source as business strategy. ron goldman, richard p. gabriel.
"If you're even thinking of doing any security engineering, you need to read this book" โ bruce schneier
secure programming techniques. gene spafford, simson garfinkel, alan schwartz.