MobileESP is an open source project for easily detecting users browsing the web pages with a mobile browser.

It has server-side versions for PHP, ASP.NET, Java, Ruby and a client-side JavaScript version with light features.

There are methods provided for detecting a specific device (iPhone, Android, WebOS, etc.) or a wider selection if it is a smartphone, tablet, game console, etc.

The project has support for most of the well-known devices and can even identify their capabilities.

Ruby on Rails is an impressive development platform which is used widely by developers and popular apps.

If you're already experienced with it, preparing the development environment it requires is pretty easy. However, if you're new to Rails, it can be tricky.

Rails Installer is a free installation package which includes everything needed for a full Rails stack (Ruby, Tails, Git, Sqlite, Devkit).

Currently, it is compatible with Windows but Mac and Linux versions are mentioned to be "coming soon"

Holla is an open source group chat application where you can create channels, invite friends to those channels, chat and share files.

It has a totally Ajaxed interface on every level (messaging, uploading files, etc.).

A nice feature is that the file uploads can be done via drag'n drops and every user in the chat can see the upload progress bar.

Holla uses Node.js for the real-time chat and falls back to Comet and Flash Sockets if WebSockets is not supported.

The application is actually a "sample resource" for the upcoming book of the author -which on asynchronous interfaces- and has a demo too.

Diaspora is an open source social networking application that is considered to be a Facebook alternative by many sources.

It includes most of the features to be expected like friendships, status messages, photos, etc.

The application's most original part is the way the user-data and so the privacy is handled: all personal data is stored wherever you want like on an hosting account or on your personal computer.

And, considering it is open source, users will be able to attach their profiles (including all personal data) to a network built with the system.

Diaspora is built with Ruby and still in the early development phase. However, seems like we'll be hearing more about it in the near future.

BBYIDX is an open source application, written with Ruby, for collecting ideas of users on specific subjects.

Actually, it is built and supported by Best Buy and also the basis behind the Best Buy IdeaX.

It enables users to post, tag, comment and vote on ideas which is a great way of mixing your community with the development flow.

Besides single ideas, categories (currents) can be created to collect a set of ideas about a specific subject.

Admins can moderate incoming ideas and comments as well as assign work-flow to certain ideas for further exploration.

The application comes with a read-write API for reaching it via a 3rd party application.

Bowline is an open source framework (not a platform like Adobe AIR or Titanium) for creating desktop applications with Ruby, HTML and JavaScript.

It respects MVC, views can be designed in HTML5/CSS3 and then you can bind them to your Ruby models.

There's no request/response cycle. Any changes in models automatically get reflected in the view.

Applications built with Bowline currently works in Mac OS X + Linux and Windows support is on the way.

Deltacloud is a Ruby gem which removes the differences between APIs of various cloud service providers and offers a single API that can communicate with them.

It is a simple and easy-to-use REST API which already supports Amazon EC2, GoGrid, Rackspace, OpenNebula, RimuHosting and more.

There is also an open source and web-based interface, Deltacloud Aggregator, which enables you to:

• view image status and stats across clouds, all in one place
• migrate instances from one cloud to another
• manage images locally and provision them on any cloud

The API is great for any Ruby developer who is using cloud services as there may always be a need for switching providers.

JsChat is an open source chat script that is built with Ruby (Sinatra), uses a simple protocol based on JSON and comes as a server/client application.

It is similar to IRC but simpler and has very useful features like:

• IRC-like commands: /names, /name new_name (/nick works too), /clear, /lastlog
• auto-linking: pasting an image displays it inline, Youtube and Vimeo videos will appear as well
• last messages are displayed when logged in

Users can "login to" or create multiple chatrooms (and they will be saved when logged out).

And, optionally, users can authenticate with their Twitter profiles.

Rhodes is an open source framework for building native applications for all major smartphone operating systems: iPhone, Windows Mobile, RIM, Symbian and Android using Ruby as the development language.

It has access to native device capabilities such as GPS geolocation, PIM contact reading/writing and camera image capture.

Development process can be called as "easier" with Rhodes as most of your UI customization can be done in HTML templates.

There are integrated styling libraries for matching the look and feel of native applications (ex: for iPhone, it is based on iUI and jQTouch can be used as well).

After The Deadline is a project of Automattic (the creator of WordPress) which checks:

• spelling
• grammar
• styles (finds complex phrases, cliches, bias-language & suggests simple ones)
• and detects misused words (has a database of 1500 most misused words & suggestions)

The software used to come as a plugin for several projects (like WordPress, RoundCube, PHP List) but it is now open source and anybody can embed it to their own code.

Besides the artificial intelligence it already has, it is possible to add new rules & improve the application.

The project also has libraries for jQuery, Ruby & Python to make developing new plugins easier.