For our own development projects, we did a lot of research before selecting Ruby on Rails as the best choice for fast, incremental web application development.
Rails supports a rapid, iterative development process and integrates easily with rich-media frameworks, including Adobe Flex, Adobe Flash and Ajax (javascript). Additionally, Rails makes it particularly easy to deploy REST APIs, which are useful for platforms that need to incorporate data from many data sources, and export information in many form factors (e.g. desktop, iphone).
Before using it on client projects, we developed Assembla Workspaces in Ruby-on-Rails to hone our own knowledge and skills in developing and deploying a complex and scalable application in Ruby. Assembla Workspaces was launched in 2006 and is used daily by hundreds of development teams for their distributed development projects.