PythonAnywhere!

Cloud9 is a code editor and development environment built with browser technology yet with the power of a desktop IDE. It's available both as an online service and as a locally hosted platform.

Heroku is a cloud application platform for Ruby, Rails, Node.js, Java, Python, Scala and Clojure web apps. Everything you need to build, run, and scale:

ideone.com is a... pastebin. But a pastebin like no other on the Internet. More accurate expression would be "online mini IDE and debugging tool".

Google App Engine is a free* platform for developing and hosting web applications in Google-managed data centers. App Engine offers fast development and deployment; simple administration, with no need to worry about hardware, patches or backups; and effortless scalability.

Codeanywhere is a code editor in a browser with a powerful ftp client integrated, and all popular web formats are supported (HTML, PHP, JavaScript, CSS, and XML).

Codiad is an open source, web-based, cloud IDE and code editor with minimal footprint and requirements

Koding is a developer community and cloud development environment where developers come together and code in the browser – with a real development server to run their code. Developers can work, collaborate, write and run apps without jumping through hoops and spending unnecessary money. The Cloud Development Environment

Nanobox is the ideal platform for developers.

ICEcoder is a browser code editor which provides a modern approach to building websites. By allowing you to code directly within the web browser, online or offline, it means you only need one program (your browser) to develop sites, plus can test on actual web servers. After development, you can also maintain the website easily, all of which make for speedy and smart development.

ShiftEdit is a free web based IDE.Features: Syntax highlighting, Integrated (S)FTP, Tabs, Find/Replace, Revision history, bookmarks.

Powerful, Collaborative Online/Offline web IDE

Google Cloud platform enables you to build and host web apps on the same systems that power Google applications. App Engine offers fast development and deployment; simple administration, with no need to worry about the underlying infrastructure and systems, patches or backups, and 99.95% SLA for business users; and effortless scalability from hundreds to millions of users.

Codenvy let's developers contribute to a project in seconds without installing software. Modify, run and debug code in the cloud or on-prem with no software to install.

Online-php.com is a free online IDE for editing files on an FTP server. The application was created for fast, free, simple and convenient read/write access to the files on FTP server. Sometimes, for some purposes, the direct FTP access is blocked and there is no conventional way to access the files on the server. This is the main reason for this WebApp.