Altus Metrum: Open hardware and software designs for high powered model rocketry by Bdale Garbee and Keith Packard. The site leads to all things about model rocketry with links to vendors, clubs, gear, and research material.
Advanced Circuits is a site referenced from the previous one. Advanced Circuits provides all manner of custom printed circuit production.
Gargoyle: free firmware upgrade for your wireless router: monitor bandwidth, set quotas and throttles, block forbidden websites, .... (alternative to dd-wrt, tomato, ..)
ArduPilot: is an open source autopilot system supporting multi-copters, traditional helicopters, fixed wing aircraft and rovers.
How does PCBWay stack up as a low budget PCB fab: a maker's entry about PCB board manufacturing, delivery, and quality. Other blog entries are equally enlightening.
2018/06/11 - Adding a PCB Vendor: OshPark: Producing Perfect Purple PCBs Promptly
2020/03/29 - lasergist - Your custom design in pure, laser-cut Stainless Steel.