Atheos is a web-based IDE framework with a small footprint and minimal requirements, built on top of Codiad by FluidByte and the Codiad Team.
Cost / License
- Free
- Open Source
Application types
Platforms
- Mac
- Windows
- Linux
- Online
- Self-Hosted


fastpen is described as 'Fastpen is an open source alternative to codepen that just stores the source code compressed, in the url' and is a Code Editor in the development category. There are more than 25 alternatives to fastpen, not only websites but also apps for a variety of platforms, including Self-Hosted, Android, Mac and Windows apps. The best fastpen alternative is Replit, which is free. Other great sites and apps similar to fastpen are CodePen, jsFiddle, JSPad and JS Bin.
Atheos is a web-based IDE framework with a small footprint and minimal requirements, built on top of Codiad by FluidByte and the Codiad Team.









ShiftEdit is the most popular commercial alternative to fastpen.
Publish HTML quickly with open source web editor, HTMLhouse. Use the editor / real-time preview to build your HTML page, and press publish when you're done. That's it! No sign up, no fuss.

Pinocode is an Offline code playground for frontend development right in your browser. It provides you a cool environment to practice frontend development using HTML, CSS and JavaScript. With support for variants and external libraries inclusion.


A full-fledged, embeddable, online editor for private, offline web projects. Integrates with Github, and is also mobile friendly!.

HTCSJS is an online HTML, CSS and JavaScript coding tool. It functions on mobile (unlike JSFiddle), and allows any* external resources. It also allows pasting on iOS, unlike many others. http://shhnowisnottheti.me/demo/
*varies b/c it uses data URLs




Pastitude is free paste hosting service. Syntax highlighting, multiple tabs, encrypted pastes, self-destruction upon opening or by time, that are all features of Pastitude.com and everything is free.

Web Maker is an easy, quick and offline web experiment playground available as a Chrome extension, with open source code available at GitHub.




A web-based IDE to teach programming in the classroom. Easily create and share exercises with students. Analyze and inspect students' submissions.

