I'd like to see the following added:

*Build your own firmware/bootloader

*Build your own FPGA/ASIC

*Build your own sound library/engine/driver

*Build your own GUI Toolkit/graphics library

*Build your own font (vector and bitmap)

*Build your own character encoding standard (à la ASCII, Unicode, etc.)

*Build your own MMO

*Build your own protocols

*Build your own mouse

*Build your own keyboard

*Build your own mail client and server

*Build your own VoIP client (à la Discord, Skype, etc.)

*Build your own instant messenger ( à la IRC, AOL, etc.)

*Build your own programming language

*Build your own markup/typesetting language

*Build your own compiler, interpreter and assembler

*Build your own machine code & microcode

*Build your own filesystem

*Build your own softmodem

*Build your own SDR

*Build your own BBS

*Build your own painting application/photo editor

*Build your own internet browser

*Build your own cryptography

*Build your own compression algorithms

*Build your own webcam and webcam client

*Build your own virtual voice assistant

*Build your own girlfriend ;)