CollapseOS is a project to make an operating system and tools that can help restart technology after a civilization collapse: https://collapseos.org/
Of course, the software is only part restarting computer technology. The other part is building things like transistors or vacuum tubes and turning those into computers.
If you only had one book to take back, I would recommend Understanding Digital Computers by Paul Siegel, which includes overviews of how transistors, vacuum tube, magnetic core memory and other things work. It shows how to make memory and logic gates from these, and how to put them together into a full computer. And more importantly the 1961 edition of this book does not seem to have the copyright renewed (checked at Stanford and LOC) so it is public domain and available at: https://archive.org/details/understanding_digital_computers
Of course, you might want more detail if you have to recreate computers, since manufacturing something with feature size smaller than a millimeter and control of the composition at better than parts per million. So I made a list of books that I believe are public domain (either because they were written by the government or because they are US books publish 1963 or before and the copyright was not renewed). This list includes ones with much more detail on transistors, vacuum tubes, magnetic core memory and also basic materials and science information that can be useful.
General Computer Information:
- Understanding Digital Computers https://archive.org/details/understanding_digital_computers
- Electronic Computers: A Made Simple Book https://archive.org/details/electronic_computers_made_simple
- Digital Computer Components and Circuits https://archive.org/details/digital_computer_components_and_circuits
Numbers with Computers:
- Arithmetic Operations in Digital Computers https://archive.org/details/arithmetic_operations_in_digital_computers
- Introduction to Numerical Analysis https://archive.org/details/introduction_to_numerical_analysis_hildebrand
Transistors:
- Transistor Circuit Analysis and Design https://archive.org/details/transistor_circuit_analysis_and_design
- TM11-690 https://radionerds.com/images/0/01/TM_11-690_BASIC_THEORY_AND_APPLICATIONS_OF_TRANSISTORS.pdf
- Transistor Technology Volumes 1 to 3:
https://archive.org/details/transistor_technology_v1
https://archive.org/details/transistor_technology_v2
https://archive.org/details/transistor_technology_v3 - Semiconductors https://archive.org/details/semiconductors_hannay
Vacuum Tubes:
- Theory of Thermionic Vacuum Tubes https://archive.org/details/Theory_of_Thermionic_Vacuum_Tubes_E._Leon_Chaffee_Ph.D._1933
- TM11-662 https://archive.org/details/TM11-662
Alternative Computer Construction:
- Digital Applications of Magnetic Devices https://archive.org/details/digital_applications_of_magnetic_devices
- Relay Engineering https://archive.org/details/relay_engineering_1962
Basic Science:
- Principles of Chemistry https://archive.org/details/principles_of_chemistry_1963
- Elementary Quantum Mechanics https://archive.org/details/elementary_quantum_mechanics_fong
- Introduction to Theoretical Physics https://archive.org/details/introduction_to_theoretical_physics_wangsness
Materials:
- Metals Handbook 1948 https://archive.org/details/metals_handbook_1948
- Metals and Plastics https://archive.org/details/metals_and_plastics_1947
This list is unfortunately missing the technology that made computers cheap in the 1970s: mask produced integrated circuits using complementary metal oxide semiconductors (CMOS), since that was just starting to be developed in 1964 when copyright still applies. (Transistor Technology Volume II chapter 9 discusses field effect transistors and Transistor Technology Volume III chapter 5 discusses photo engraving which are precursors technologies.)
Never the less, having a paper copy of these books would help you greatly should you ever wish to restart computer technology after a civilization collapse.
Update (2021-October-1):
Additional public domain books and papers.
CMOS article:
- DTIC ADA033080: Introduction to Custom CMOS LSI's for Digital Logic https://archive.org/details/DTIC_ADA033080
Printing and Engraving (Similar techniques to photo-lithography for integrated circuits):
- Circular of the Bureau of Standards no. 565: https://archive.org/details/circularofbureau565davi
- Microphotography https://archive.org/details/microphotography_1957
Transistor engineering and physics:
- Transistor Engineering and Introduction to Integrated Semiconductor Circuits https://archive.org/details/transistor_engineering_1962
- Semiconductor Device Physics https://archive.org/details/semiconductor_device_physics_1962
Logic design:
- Digital Computer Design Fundamentals https://archive.org/details/digital_computer_design_fundamentals_chu
- The Logic Design of Transistor Digital Computers https://archive.org/details/the_logic_design_of_transistor_digital_computers_1963
- Switching Circuits with Computer Applications https://archive.org/details/switching_circuits_with_computer_applications_humphrey
More Math:
- Boolean Algebra and Its Applications https://archive.org/details/boolean_algebra_and_its_applications_1961
- Elementary Mathematics from an Advanced https://archive.org/details/elementary_mathematics_arithmetic_algebra_analysis and https://archive.org/details/elementary_mathematics_geometry
Integrated Circuits:
- Introduction to Integrated Semiconductor Circuits https://archive.org/details/introduction_to_integrated_semiconductor_circuits_1963
- Semiconductor Fundamentals Devices and Circuits https://archive.org/details/semiconductor_fundamentals_devices_and_circuits_1963
Dictionary of Applied Physics (From the 1920s, but comprehensive):
- https://archive.org/details/in.ernet.dli.2015.152557
- https://archive.org/details/in.ernet.dli.2015.176701
- https://archive.org/details/dli.bengal.10689.570
- https://archive.org/details/in.ernet.dli.2015.212412
- https://archive.org/details/in.ernet.dli.2015.37757
P.S. TM11-690 is also at archive.org: https://archive.org/details/tm_11_690_theory_and_application_of_transistors
