Ruby on Rails is a great development framework. Built on top Ruby it is geared specifically for web development. Powerful web applications that would take months or years in other languages can be completed in a matter of hours using Ruby on Rails.

Best for:

Data Driven websites or websites with multiple front ends

Famous examples

Hulu, Scribd, and Github

PHP is a well established language on the web. Most small to medium sites make their first leap from static HTML to data driven content utilizing PHP.

Best for

Mostly static sites that need a touch of data driven content

Famous Examples

Wikipedia and Facebook

Android is a Linux based mobile platform used in everything from eBook readers to cellphones. It's open source policies and Google backing make this the platform of choice for both business and personal use. Android applications are developed in Java, and deploy, most of the time, using the built in Android market.

Best for

Any application where you want users to interact with your data via their mobile device that runs Android (cell phones, tablets, and other mobile devices)

Famous Examples

Paypal, Uber

The iPhone is a staple in the mobile phone industry, and Apple's iPad, is quickly becoming a staple in many homes. Like the Android, the iOS devices have a built in App market for distributing your application.

Best for

Any situation where you want you users to interact with your data via their iPhone or iPad

Famous Examples

Rdio, Air Video

ASP.NET is Microsoft's leading language for website development. While not as fast a development platform as Ruby on Rails, and not as wide spread as PHP, ASP.NET has definitely earned it's place as the web language of choice for "Microsoft Shops".

Best for

Web applications that are housed on IIS servers

Famous Examples

Microsoft.com

Sometimes you just want a quick site, blog, or something basic for an existing business. In many cases a pre-built system already exists. Why develop a blog when you can just install WordPress.

Best for

Sites that want to stay in a tight budget or are wanting functionality close to existing systems (a blog or forum for example)

Famous Examples

Worpress, Drupal, and Joomla

While defiantly an aging language, ASP was the main-stream language for a long time. Most ASP Classic projects these days involving maintaining older sites or converting old sites to newer languages.

Best for

Sites that need a tiny amount of scripting, but are on IIS servers where PHP is not available

HTML is the core of every site on the web. If you just want some static content then you can skip the programming languages and just use plain, old fashion, markup.

Best for

Static content that never changes, and one off pages that will never change

Famous Examples

Every site uses html in some form, but most are dynamic (thus needing a programming language).