Here is a list of some open source tools for your web Development Systems.
1. ASP.NET: ASP.NET is an open source web framework for building modern web applications and services. With ASP.NET you can quickly create websites based on HTML, CSS, and JavaScript, scale them to millions of users and easily add more complex capabilities like Web APIs, forms over data or real time communications.
Download: http://www.asp.net/downloads
Operating System: Windows, Linux, OS X.
2. Bluefish : Bluefish is a powerful editor targeted towards programmers and web developers, with many options to write websites, scripts and programming code. Bluefish supports many programming and markup languages.
Download: https://sourceforge.net/projects/bluefish/
Operating System: Windows, Linux, OS X
3. Bootstrap: Bootstrap is the most popular HTML, CSS, and JS framework for developing responsive, mobile first projects on the web. Bootstrap makes front-end web development faster and easier. It's made for folks of all skill levels, devices of all shapes, and projects of all sizes.
Download: http://getbootstrap.com/
Operating System: OS Independent
4. Bower: Bower can manage components that contain HTML, CSS, JavaScript, fonts or even image files. Bower doesn’t concatenate or minify code or do anything else - it just installs the right versions of the packages you need and their dependencies. Bower works by fetching and installing packages from all over, taking care of hunting, finding, downloading, and saving the stuff you’re looking for
Download: https://github.com/bower/bower
Operating System: OS Independent
5. Brackets: Brackets is a lightweight, yet powerful, modern text editor. It blends visual tools into the editor so you get the right amount of help when you want it without getting in the way of your creative process.
Download: http://www.softpedia.com/get/Programming/File-Editors/Brackets.shtml
Operating System: OS Independent