These softwares and web services are widely used in makers projects. They are open source, and most don’t require signing up.

Linux Debian Ubuntu an Operative System https://www.ubuntu.com/desktop

Inkscape a Vector Graphics Editor https://inkscape.org

FreeCad a parametric 3D modeler https://www.freecadweb.org

Fritzing an Electronic Design Automation http://fritzing.org/

Saas

Create an App to connect to Bluetooth connected board: App Builder MITApp http://ai2.appinventor.mit.edu/

http://ai2.appinventor.mit.edu/images/codi_long.png?t=1527782184105

Upload code directly from web based Arduino editor IDE https://create.arduino.cc/

Websites

Statics websites with Hugo https://gohugo.io/ and a GUI third party service https://app.forestry.io

Hugo on PC, upload files on Github, get Github files from Forestry, manage web on forestry push changes on github, link github to custom domain

creating contact form https://formspree.io/ no account needed

using comment services https://disqus.com/ (ads supported)