You might want to try
display simultaneously file tree and editor area (and be able to switch between files); CHECK
support markdown format (highlight markdown format and display formatted preview); CHECK
(nice to have) be able to display TOC generated from markdown headers in file; CHECK
be open source and work under Linux. CHECK
Discord is free and the most popular team communication app for gamers. The platform provides users with familiar Slack-like UI, Skype-like video, and voice chats. Discord is amazing to use while participating in a Dota 2 battle, but it also meets collaboration challenges many companies face.
The tool divides channels by text and voice. ...
Mattermost is the main alternative to Slack that covers most of your requirements. I have not looked at it in a while, but you will also find a few useful others here in previous questions:
Team chat with private rooms, file upload and link previews (alternative to Slack)
Team chat with native Android/iOS apps, all open source (alternative to Slack)
I recommend you to try Fastreel. For creating a video you need - add your files, select the transition style and set the image display duration, if it's necessary add audio track (or choose one from the library) and save the result.
For 3D shapes, https://www.allwinedesigns.com/blog/stlcmd is notable.
It can draw cubes, spheres, cylinders, cones, toruses, threads (the goal was to provide a tool for 3D printing). There's a transform tool which can scale uniformly and also along any angle. Another tool will do intersections, union and differences.
The output is in STL format, http://...
Auth0 does this without entering a code. Their docs even say:
This link will allow them to login directly when clicking on it. It is similar in function to them getting an email with a one-time-use code in it, returning to your app, and entering the code, **but without having to actually perform those steps**.
If you want to run this service yourself, not a ...
Moodle can easily be integrated at country level and the limitation is usually in how well your underlying infrastructure handles the load - The app itself is pretty solid and will work well for a pretty huge userbase.
I found a tutorial of adding a real-time google translation button for pdf-xchange editor.
Although pdf-xchange editor is not open source software, but I think it is a good hint for other pdf viewers.
You can download PDF-XChange Editor free version here
It isn't very clear from your question if you are looking to just make layout i.e. wireframe or you want to create the whole website by drag and drop. Assuming the latter, you could try https://grapesjs.com/
GrapesJS is an open-source, multi-purpose, Web Builder Framework which combines different tools and features with the goal to help you (or users of ...
For creating "windows with forms, buttons, labels, etc" as you say, sounds like this may meet your needs:
It's not super complex, but can certainly make buttons, labels, progress bars, and other things. It lets you create Python 3 Tkinter GUIs right in your browser, and displays the Python code in a column on the right-hand side....
I do not have personal experience using these programs, but I did find the following possibilities. Symphytum is free and open source personal database software. It runs on Windows, Linux and MacOS. It looks pretty nice. Another I'm aware of is KEXI. It attempts to rival MS Access and Filemaker while being open source. It is available for Windows and Linux ...