Zeal is an offline software documentation browser covering almost 200 APIs, languages, applications and tools: ActionScript, Android, Apache, Bash, CSS, C++, Docker, Java, JavaScript, Lua, Mono, MySQL, NET Framework, OS X, OpenGL, PHP, Python, Qt, Vim, Wordpress and many others.

The download doesn't include any of these, but they're simple to download. Go to File > Options > Docsets, check the boxes next to anything interesting in the "Downloadable docsets" box and click Download.

Whatever you're chosen is displayed in a tree. Expanding the HTML docset reveals references for 484 attributes and 138 tags, for instance, while the Apache HTTP Server covers commands, directives and modules, as well as 81 guides on topics like .htaccess files and "When NOT to use mod_rewrite".

Alternatively, you're able to type a query like "html:bgcolor" to see the relevant page. (Zeal displays matches as you type, for easier access.)

Some editors and IDEs have plugins enabling access to Zeal from within their products. Atom, Brackets, Emacs and Sublime Text are just a few examples.

Zeal 0.3.1 brings fixes for several important problems, such as random crashing for users of Ubuntu Unity and other AppIndicator-based desktop environments, and application freezing on Windows.

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Simple and straightforward references for developers, also faster and more responsive than you'll get from most browser-based equivalents.