Here are 100 low-cost prototyping boards with user communities, open source software, and their best URLs for documentation or main open source repositories:

  1. Arduino Uno - https://www.arduino.cc/en/Guide/ArduinoUno
  2. Raspberry Pi Zero - https://www.raspberrypi.org/documentation/rp2040/getting-started/
  3. ESP8266 - https://github.com/esp8266/Arduino
  4. ESP32 - https://docs.espressif.com/projects/esp-idf/en/latest/esp32/
  5. BBC micro:bit - https://microbit.org/get-started/user-guide/overview/
  6. Adafruit Circuit Playground Express - https://learn.adafruit.com/adafruit-circuit-playground-express
  7. Particle Photon - https://docs.particle.io/photon/
  8. Teensy 4.0 - https://www.pjrc.com/store/teensy40.html
  9. STM32 Nucleo-64 - https://www.st.com/en/evaluation-tools/stm32-nucleo-boards.html
  10. TI LaunchPad - https://www.ti.com/tool/MSP430-LAUNCHPAD
  11. PIC32 Curiosity - https://www.microchip.com/developmenttools/ProductDetails/DM320103
  12. Intel Edison - https://software.intel.com/content/www/us/en/develop/articles/intel-edison-developer-resources.html
  13. BeagleBone Black - https://beagleboard.org/black
  14. Onion Omega2+ - https://docs.onion.io/omega2-docs/
  15. Seeed Studio XIAO - https://wiki.seeedstudio.com/Seeeduino-XIAO/
  16. SparkFun Thing Plus - https://learn.sparkfun.com/tutorials/esp32-thing-plus-hookup-guide
  17. Cypress PSoC 6 BLE Pioneer Kit - https://www.cypress.com/documentation/development-kitsboards/psoc-6-ble-pioneer-kit-cy8ckit-062-ble
  18. Nordic nRF52840 DK - https://www.nordicsemi.com/Software-and-tools/Development-Kits/nRF52840-DK
  19. Sipeed Maix Bit - https://maixduino.sipeed.com/en/
  20. Giant Board - https://www.crowdsupply.com/groboards/giant-board
  21. Adafruit Feather M0 Express - https://learn.adafruit.com/adafruit-feather-m0-express-designed-for-circuit-python-circuitpython
  22. Espressif ESP32-S2-Saola-1 - https://docs.espressif.com/projects/esp-idf/en/latest/esp32s2/hw-reference/esp32s2/user-guide-saola-1-v1.2.html
  23. LoRa32u4 II - https://github.com/BLavery/LoRa32u4-II
  24. Bluz DK - https://docs.bluz.io/
  25. Mbed LPC1768 - https://os.mbed.com/platforms/mbed-LPC1768/
  26. Teensy 3.6 - https://www.pjrc.com/store/teensy36.html
  27. Wemos D1 Mini - https://www.wemos.cc/en/latest/d1/d1_mini.html
  28. NodeMCU - https://nodemcu.readthedocs.io/en/release/
  29. Pycom WiPy - https://docs.pycom.io/gitbook/assets/wipy-pinout.pdf
  30. LilyPad USB - https://www.arduino.cc/en/Main/ArduinoBoardLilyPadUSB/
  31. Nano 33 BLE Sense - https://www.arduino.cc/en/Guide/NANO33BLESense
  32. Hexiwear - https://www.mikroe.com/hexiwear
  33. Rocket Scream Mini Ultra - https://github.com/rocketscream/MiniUltraLoRa
  34. Heltec WiFi Kit 32 - https://heltec.org/project/wifi-kit-32/
  35. TTGO T-Beam - https://github.com/LilyGO/TTGO-T-Beam
  36. Adafruit HUZZAH32 - https://learn.adafruit.com/adafruit-huzzah32-esp32-feather
  37. M5Stack Core - https://docs.m5stack.com/#/en/core/basic
  38. Seeeduino Lotus - https://wiki.seeedstudio.com/Seeeduino_Lotus/
  39. Sipeed Longan Nano - https://longan.sipeed.com/en/
  40. MakerFocus ESP32 Audio Kit - https://github.com/MakerFocus/ESP32-Audio-Kit
  41. Wio Terminal - https://wiki.seeedstudio.com/Wio-Terminal-Getting-Started/
  42. Adafruit ItsyBitsy M0 Express - https://learn.adafruit.com/introducing-itsy-bitsy-m0
  43. Particle Argon - https://docs.particle.io/argon/
  44. Adafruit Trinket M0 - https://learn.adafruit.com/adafruit-trinket-m0-circuitpython-arduino
  45. Espruino Pico - https://www.espruino.com/Pico
  46. Simblee - https://www.simblee.com/Simblee_Quickstart_Guide_v1.1.0.pdf
  47. nRF51822 Beacon Kit - https://www.nordicsemi.com/Software-and-Tools/Development-Kits/nRF51822-Beacon-Kit
  48. RFduino - https://github.com/RFduino/RFduino
  49. TinyCircuits TinyDuino - https://tinycircuits.com/pages/tinyduino-overview
  50. PyCom LoPy4 - https://docs.pycom.io/gettingstarted/connection/lopy4/
  51. Particle Boron - https://docs.particle.io/boron/
  52. SparkFun Pro nRF52840 Mini - https://learn.sparkfun.com/tutorials/pro-nrf52840-mini-hookup-guide
  53. Feather S2 - https://learn.adafruit.com/adafruit-feather-stm32f405-express
  54. Adafruit QT Py - https://learn.adafruit.com/adafruit-qt-py
  55. Seeed XIAO BLE - https://wiki.seeedstudio.com/XIAO_BLE/
  56. TinyPICO - https://www.tinypico.com/gettingstarted
  57. ESP32 PICO KIT - https://www.espressif.com/en/products/devkits/esp32-pico-kit
  58. Maxim MAX32620FTHR - https://www.maximintegrated.com/en/products/microcontrollers/MAX32620FTHR.html
  59. Nano RP2040 Connect - https://store.arduino.cc/usa/nano-rp2040-connect
  60. OrangeCrab - https://github.com/gregdavill/OrangeCrab
  61. Adafruit Metro M4 Express - https://learn.adafruit.com/adafruit-metro-m4-express-featuring-atsamd51
  62. RISC-V HiFive1 Rev B - https://www.sifive.com/boards/hifive1-rev-b
  63. Sipeed Tang Nano - https://tang.sipeed.com/en/
  64. OrangeCrab - https://github.com/gregdavill/OrangeCrab
  65. WeAct Studio Black Pill - https://github.com/WeActTC/MiniSTM32F4x1
  66. Teensy 4.1 - https://www.pjrc.com/store/teensy41.html
  67. Adafruit Feather nRF52840 Express - https://learn.adafruit.com/introducing-the-adafruit-nrf52840-feather
  68. Kittenbot Meowbit - https://www.kittenbot.cc/collections/frontpage/products/meowbit-codable-console-for-microsoft-makecode-arcade
  69. LilyGo TTGO LoRa32 V2.1 - https://github.com/LilyGO/TTGO-LoRa32-V2.1
  70. STM32WB Nucleo Pack - https://www.st.com/en/evaluation-tools/p-nucleo-wb55.html
  71. WisBlock RAK4631 - https://docs.rakwireless.com/Product-Categories/WisBlock/
  72. Sensebox MCU - https://sensebox.de/en/products-parts/parts/sensebox-mcu.html
  73. Lolin D32 Pro - https://docs.wemos.cc/en/latest/d32/d32_pro.html
  74. Hardkernel ODROID-GO - https://wiki.odroid.com/odroid_go/odroid_go
  75. Khadas VIM3 - https://docs.khadas.com/vim3/
  76. MangoPi MQ Pro - https://mangopi.org/mangopi_mq_pro
  77. NanoPi NEO3 - https://wiki.friendlyarm.com/wiki/index.php/NanoPi_NEO3
  78. UDOO BOLT - https://www.udoo.org/docs-bolt/
  79. 96Boards Consumer Edition - https://www.96boards.org/products/ce/
  80. HiFive Unleashed - https://sifive.cdn.prismic.io/sifive/1a92cb94-a921-4d1a-a8b6-3d3f75e873f0_hifive-unleashed-getting-started-guide-v1p1.pdf
  81. LinkIt 7697 - https://docs.labs.mediatek.com/resource/linkit7697-arduino/en
  82. MaaxBoard - https://wiki.solid-run.com/doku.php?id=products:imx8:maaxboard
  83. MicroPython pyboard D-series - https://store.micropython.org/pyboard-d-series-specs.html
  84. PADI IoT Stamp - https://github.com/PADI-IoT-Stamp/Documentation
  85. PocketBeagle - https://beagleboard.org/pocket
  86. Radxa Rock Pi S - https://wiki.radxa.com/RockpiS
  87. Raspberry Pi Zero 2 W - https://www.raspberrypi.org/documentation/rp2040/getting-started/
  88. SAMA5D27 SOM1 EK1 - https://www.microchip.com/developmenttools/ProductDetails/atsama5d27-som1-ek1
  89. Sipeed Maixduino - https://maixduino.sipeed.com/en/
  90. Sparky - https://www.sparkyfirmware.com/
  91. STEMTera Breadboard - https://www.stemtera.com/
  92. Tinker Board S R2.0 - https://tinkerboarding.co.uk/wiki/index.php/Main_Page
  93. UDOO X86 II - https://www.udoo.org/docs-x86ii/
  94. VoCore2 - https://vocore.io/v2.html
  95. XMC 2Go - https://github.com/Infineon/XMC-for-Arduino
  96. A-Star 32U4 Micro - https://www.pololu.com/docs/0J61
  97. BBC micro:bit v2 - https://microbit.org/get-started/user-guide/overview/
  98. Feather STM32F405 Express - https://learn.adafruit.com/adafruit-feather-stm32f405-express
  99. Franzininho WiFi - https://github.com/Franzininho/franzininho-wifi-board
  100. Serpente - https://serpente.io/docs

These resources provide a starting point for learning about each board, its capabilities, and how to get started with development using the available open-source software and community support.