Yosys — The Complete Guide: Verilog Synthesis and a Fully Open FPGA Flow
Yosys turns Verilog into a gate netlist, and with nextpnr takes you from source to FPGA bitstream without one proprietary tool. Permissive ISC licence.
Guides and Articles
GHDL — The Complete Guide: Open-Source VHDL Simulation, From the Course to the FPGA
GHDL compiles and runs VHDL so you can verify a hardware design before synthesis: VHDL-87 to 2008, waveform files for GTKWave and a link to Yosys. Fully free.
Xyce — The Complete Guide: A Parallel SPICE Simulator for Very Large Circuits
Sandia’s Xyce is an open-source SPICE simulator that spreads the solution across many cores or a cluster and handles circuits with millions of devices.
Qucs-S — The Complete Guide: Analogue and RF Circuit Simulation With a Friendly Schematic Interface
Qucs-S pairs a friendly schematic editor with proven SPICE engines like Ngspice and Xyce: DC, AC, transient, noise and S-parameters. Free for analogue and RF.
SimulIDE — The Complete Guide: Real-Time Circuit Simulation With Arduino, AVR and PIC
SimulIDE runs a circuit in real time together with PIC, AVR and Arduino chips executing your own code, plus editor, debugger, scope and serial monitor.
Falstad Circuit Simulator — The Complete Guide: Watch Current Flow Through a Circuit, Right in the Browser
The Falstad simulator shows current as moving dots and updates instantly as you edit. It runs in the browser with no install and hundreds of ready examples.
OpenTripPlanner — The Complete Guide: Free Multimodal Journey Planning and Transit Accessibility
OpenTripPlanner computes trips combining walking, cycling and transit from GTFS timetables and OpenStreetMap, for accessibility analysis and comparing plans.
OSRM — The Complete Guide: A Fast Free Road Routing Engine for Routes and Travel-Time Matrices
OSRM computes routes on the OpenStreetMap road network in milliseconds, plus time and distance matrices between hundreds of points: response times, OD matrices.
Earth Point — The Complete Guide: Coordinate Conversion and Google Earth Display, What Is Free and What Is Paid
Earth Point converts between lat/long, UTM and US systems online and shows the point in Google Earth. Basic conversions are free; some tools need a paid plan.
SurveyTools — The Complete Guide: Survey Network Adjustment, Road and Rail Alignments and Coordinate Transforms
SurveyTools is a free toolkit for surveyors and designers: network and levelling adjustment, coordinate transforms, and road, rail and tunnel alignments.
RTKLIB — The Complete Guide: Open-Source GNSS Processing to Centimetre Accuracy, RTK and PPK
RTKLIB processes raw GNSS observations to centimetre accuracy: real-time RTK, post-processed PPK and static solutions, so a cheap receiver gets survey grade.
GeoServer — The Complete Guide: Free Publishing of GIS Layers as WMS and WFS Services
GeoServer is an open-source map server that publishes GIS layers as open-standard services — WMS, WFS, WCS and WMTS — so a whole team reads from one source.