It is kinda easy to find high-quality open source web apps in PHP or JavaScript. But that’s a little harder for ASP.NET.

JabbR is one of those treasures, it is an open source ASP.NET app for real-time chats.

The app uses SignalR library for the communication and allows users to register/sign-in with their e-mails or via social auth (Facebook, Google, etc.).

Users can define an avatar for themselves and communicate in a chat room (multiple chat room support with a tabbed interface) or privately.

It can display inline content from multiple sources like YouTube, Vimeo, Twitter, imgur, Google Docs and much more.

There are multiple notification types so that you also keep up with the conversation (Chrome pop-ups, live Twitter mentions or audio).

JabbR support Emojis, has keyboard shortcuts and IRC-like commands. Also, it has a responsive layout.

On small screens, displaying a button/icon that can show/hide menu items in a single column is a very common method for responsive navigations. Even the icon used is pretty standard.

Responsive-Nav, a JavaScript plugin, simplifies creating such responsive menus with a lightweigt footprint (1.6kb minified-gzipped).

It makes use of touch events and CSS3 transitions for a great performance and works on screen readers + with a JavaScript-disabled state.

Also, the plugin is standalone and has callbacks for the init, open and close events.

Medoo is a lightweight (~8kb) PHP framework for working with SQL databases.

The framework comes as a single file and works with MySQL, MSSQL, PostgreSQL, SQLite (and more).

It has methods for all the common SQL queries and controls for preventing SQL injention.

Medoo is simple-yet-handy and it is very well-documented.

Hidden side menus are a good way of enabling users to view the navigation options on request. And, they are perfect for responsive layouts as they save space.

Sidr is a jQuery plugin for creating “hidden side menus” on-the-fly.

It can be set to be displayed at right or left, a single page can have multiple side menus and offers multiple methods (existing or remote content) for loading the content.

For responsive layouts, a Sidr menu can be attached to a button (that is displayed for specific screen sizes with media -queries) and it’ll be a very handy navigation solution for small screens.

Bespoke.js is a lightweight (<1kb minified-gzipped) JavaScript framework for crafting totally custom presentations or content sliders.

It is a foundation that offers the base (keyboard + touch support and adding the necessary classes to slide items) and the rest (CSS transitions or any other JS ) can be developed however preferred.

There is a JavaScript API provided with all the major events like next, prev, a specific slide, etc. and a plugin system exists for extending it.

Also, the demo includes awesome themes that can be find many use cases to themselves.

Swipebox is a jQuery lightbox plugin that has support for touch events and works well in responsive layouts.

It can display a single item or a group of items (gallery) where they can be browsed with swipe gestures or keyboard too.

The plugin mostly uses CSS transitions and has jQuery fallback for unsupported browsers.

Captions can be displayed with ease and few options exist for customization (like the appearance delay of the action bar)

Nested is a jQuery plugin for generating multi-column grid layouts with zero gaps.

The plugin creates a matrix of all elements, builds a multi column grid and tries to fill any gaps by reordering the elements.

There are various other solutions out there that does the same. However, Nested applies one small action: it resizes any element at the bottom of the grid to guarantee the gap-free layout.

Its usage is very easy by simply targeting a container element through a jQuery function.

And, various options exist for customization like enabling/disabling animation, min. number of columns and more.

Microsoft Excel, Google Spreadsheets and similar spreadsheet apps have powerful formula functions.

Formula.js is a JavaScript library that brings most of these formulas to web developers.

The formulas are listed under multiple categories like date/time, text, logical, financial and much more.

Also, besides client-side it works with nodejs (to be released soon) as well.

Chart.js is an impressive JavaScript charting library that is built on top of HTML5 canvas.

It currently supports 6 chart types (line, bar, radar, pie, column and polar area) and all this comes in a standalone, <5kb package.

Colors, fonts, borders and their sizes can all be customized. Also, optionally, charts can be loaded with an animation.

As the library is built with canvas, it works on a wide set of browsers, loads fast but lacks interactivity.

Extra Strength Responsive Grids is a CSS framework that comes with solutions to various issues experienced in responsive layouts.

The framework is completely grid-focused (no styles for typography, tables, forms, etc.) and uses percentage-based width adjustments.

For smaller screens, besides using less columns, elements can be resized smartly.

Also, it has support for nested grids and the framework is built on top of SASS that allows any quick customizations.