Links
Blogs
Board Retailers
Adafruit - Another retailer and designer with excellent selection and tutorials.
Sparkfun - Retailer and designer of open source electronics development boards and other equipment and materials with excellent accompanying tutorials.
Tindie - Marketplace for electronics makers to sell low volume batches of their own designs.
CAD Specific Resources
Adafruit Eagle Library - Eagle Specific
Contextual Electronics' Getting to Blinky Tutorial - KiCad Specific - A more comprehensive beginner to intermediate video tutorial.
Contextual Electronics' Shine on You Crazy KiCad - KiCad Specific - Beginner video tutorial that gets you to a manufactured board as quickly as possible.
Eagle - List of ULPs everyone should know - Eagle Specific
Eyrie.io - For viewing Eagle and KiCAD designs online
KiCad Cheatsheet - KiCad Specific - Short PDF that goes over the menus and keyboard shortcuts for the most common operations.
KiCad Footprint Collection - KiCad Specific - Collection of all the KiCAD footprints available online and some scripts to manage them.
KiCad Third-Party Tools - A curated list of third-party tools to be used in conjunction with the KiCad open-source electronics design automation suite.
KiCAD.info Forums - KiCad Specific - User discussion and help forum.
KiKit – Automation for KiCAD - KiKit is a Python library, KiCAD plugin and a CLI tool to automate several tasks in a standard KiCAD workflow
SparkFun Electronics Eagle Libraries - Eagle Specific
Xesscorp's list of KiCAD 3rd party tools - KiCAD Specific
Communities
CircuitMaker - CircuitMaker is not just a free EDA software tool from Altium, it’s also a community of creative people and design content.
Hackaday.io - Hackaday.io is the world's largest collaborative hardware development community.
Hackster - Hackster is a community dedicated to learning hardware. Need registration to view projects
Instructables - Instructables is a place that lets you explore, document, and share your creations.
Maker.io - Maker.io is a hardware development community powered by Digi-Key Electronics.
Maker.pro - Maker.pro is a place for makers to design and collaborate with one another, with the goal to take their product to market.
Crowdfunding
Footprint Repositories
Forums
/r/askelectronics - Sub-reddit dedicated to help on electronics topics.
/r/electronics - /r/electronics and /r/ECE are the two most active sub-reddits for EE topics.
EEVBlog forum - Probably the largest and most active forum to discuss electronic engineering topics.
Electronics Stack Exchange - Question and answer site for electronics running on the popular Stack Overflow service.
Electronics-Talk.com - A new, powerfull community that is quiet for the moment
Free EDA Packages
Altium Circuit Maker - Free package from the maker of the go to pro software.
Caneda - Caneda is an open source EDA software suite focused on ease of use and portability.
Design Spark PCB - Gratis EDA package without restrictions, sponserd by RS Components.
DipTrace - Quality Schematic Capture and PCB Design software with (pin and signal layer restricted) free version.
Eagle - One of the most popular EDA packages due to it's (board size restricted) free version.
EasyEDA - Online PCB Design Tool
EXPRESSPCB - ExpressPCB has been THE free PCB layout and design software for over 20 Years, used by Engineers, electronic Designers, students and hobbyists.
Fritzing - Fritzing is an open-source initiative to develop amateur or hobby CAD software for the design of electronics hardware.
gEDA - Another open source package, good for people that like scripting and makefiles, Linux and BSD only.
KiCAD - Open source EDA package with push and shove router, differential pairs and much more.
LibrePCB - A new, powerful and intuitive EDA tool for everyone, cross-platform and GNU GPLv3.
Pad2Pad - Free PCB layout software connected to a REAL circuit board manufacturer.
PCB123 - Design tool for Printed Circuit Board designers of all levels
PCBWeb - Free CAD application for designing and manufacturing electronics hardware
Upverter - Upverter is an EDA system delivered in a web-browser which enables hardware engineers to design, share, and review schematics and PCBs
ZenitPCB - CAD software for schematic and printed circuit board design.
Gerber Viewers
CircuitPeople - View and share gerber files for your PCB design online
EasyEDA Gerber Viewer - Gerber viewer and design for manufacture test.
GC-Prevue - Industry standard software for viewing manufacturing data
Gerblook - Online Gerber viewer powered by Gerbv.
Gerbv - Excellent Gerber viewer for Linux and BSD. (Installable)
KiCAD Gerbview - The KiCAD gerber viewer. (Installable)
Mayhew Labs 3dpcb - 3D Gerber viewer.
Pentalogix ViewMate - Gerber viewer and editing workhorse
Tracespace Viewer - Gerber viewer that lets you inspect the individual layers as well as the board preview.
Viewplot - The Gerber viewer, Editor & Converter in one
ZofZPCB - Lets you see inside your board
Inventory Management
Part-DB - Another open source web service for managing part inventory with a permission system and a good barcode generator.
Partkeepr - Open source web service for managing your part inventory with parametric search and automatic datasheet import.
Partsbox.io - Web service to manage your part inventory with a nice user interface and Octopart integration.
Microcontrollers
AVRDUDE - AVRDUDE is a utility to download/upload/manipulate the ROM and EEPROM contents of AVR microcontrollers using the in-system programming technique (ISP).
AVRDUDESS – A GUI for AVRDUDE - AVRDUDESS is a GUI for AVRDUDE, a tool for programming Atmel microcontrollers.
Embedded Lab - Embedded Systems tutorials, projects, Arduino, ESP8266, Microchip PIC and more ...
WinAVR - WinAVR (tm) is a suite of executable, open source software development tools for the Atmel AVR series of RISC microprocessors hosted on the Windows platform. Includes the GNU GCC compiler for C and C++.
Part Search Engines
Parts 3D Models
3D ContentCentral - 3D ContentCentral is a free service for locating, configuring, downloading, and requesting 2D and 3D parts and assemblies
AutoDesk Library.io - Parametric ECAD - MCAD content generation online
GrabCAD - GrabCAD is the largest online community of engineers, designers, manufacturers & students.
traceParts - A huge choice of 3D models, CAD files and 2D drawings. It's free!
Parts Purchase
LCSC - Shenzhen based parts supplier with great prices
Pololu - Robotics and Electronics from USA
PwnKitteh/InsanelyCheapElectronics - A list of cheap electronics from China, that you can use in your projects
Unikeyic - Unikey is a global authorized distributor and stockist specializing in high-quality electronic components.
WIN SOURCE - Obsolete Electronic Components Distributor
PCB Batching Services
Aisler - Affordable quality circuit boards made in and shipped from Europe (Germany).
Dirty PCBs - Low cost PCB batching service that prides itself on its "dirty" quality.
OSH Park - Low cost PCB batching service with high quality boards with a signature purple silkscreen.
PCB Shopper - Comparison service for quite a lot of different PCB batching and assembly services.
PCB Design Software at a cost
Altium Designer - Combines precision, usability, Native 3D, and collaboration to enable engineers and designers to get complex PCB designs done right, the first time.
Autodesk EAGLE - Flexible, expandable and scriptable application with schematic capture editor, PCB layout editor, auto-router etc. Free version is available
CADENCE ALLEGRO - Takes simple or complex designs from concept to production in a constraint-driven design system.
CADSTAR - Complete design environment for PCB design – from initial concept through to product realization.
CometCAD - Circuit schematic and layout editor program for Windows 2k, XP, Vista and 7.
DIPTRACE - Software for creating schematic diagrams and printed circuit boards.
EASYPC - Delivering performance in Schematic Capture and PCB Layout normally associated with products at ten or even twenty times the price.
MENTOR - Design Software and Tools offers a comprehensive suite of solutions that improve design, accelerate time to market & increase profit margins.
OrCAD - Suite of products for EDA, and includes a schematic editor (Capture), a circuit simulator (PSpice) and a PCB designer.
PADS - The industry-leading, high-productivity, PCB-centric design solution for independent engineers.
PULSONIX - Choose a combined SCM/PCB product, or Schematic only option.
Project Sharing
Simulators
Circuit JS - Open source online simulator for simpler circuits with live interactivity and visualization.
Circuit Sandbox - Javascript Circuit Simulator with basic capabilities
CircuitLab - CircuitLab is an in-browser schematic capture and circuit simulation software tool to help you rapidly design and analyze analog and digital electronics systems.
Every Circuit - Free to try online, visual, interactive circuit simulator for simpler circuits.
iCircuit - Easy to use electronic circuit simulator, its advanced simulation engine can handle both analog and digital circuits and features realtime always-on analysis.
LTSpice - The industry standard free SPICE circuit simulator from Linear Technologies.
Multisim - Multisim is industry-standard SPICE simulation and circuit design software for analog, digital, and power electronics in education and research (National Instruments)
Ngspice - Open source SPICE circuit simulator.
PartSim - Online Circuit Simulator
Qucs - Open source integrated circuit simulator for DC, AC, S-parameter, noise analysis, etc.
Theory and Courses
All About Circuits - Online textbook for learning theory with clear diagrams and explanations.
Electrical Engineering - Khan Academy - Online learning platform with lots of topics, including a full course on electrical engineering, circuits, semiconductors, signals, robots, and even reverse engineering electronic devices.
ElectronicsTutorials - The purpose of this site is to give students and beginners alike studying Electronics, good Basic Electronics Tutorials and information to help develop a knowledge and understanding of the subject of Electronics.
Elliott Sound Products - The home of DIY audio articles with great schematics and explanation
FreeVideoLectures/Electronics - Free Video Lectures from top Universities.
Videos
EEVblog - One of the earliest and most successful YouTube channels where Dave Jones does teardowns, tutorials and more.
GreatScott! - Awesome Electronics Tutorials, Projects and How To´s.
The Signal Path - Very in depth teardowns, repairs and reviews of lab equipment and prototyping products.
Voltlog - Teardowns and review videos