RDI comes in three versions:
Rational Developer for i RPG and Cobol Tools
This is the tool for the classic i Developer who wants to build green screen applications with RPG and Cobol. Also included is a graphical Version of SDA and plugins to access the db2 on i. There is no support for Web development in this version from Rational, although you can add open source plugins from Eclipse to fill the gap.
Rational Developer for i RPG and Colbol + Modernization Tools
This version has all of the Basis version with many additional plugins to build Web Applications on the Websphere software stack from IBM. Many of this plugins are very complex and need highly trained developer on this tools to be productive. The are very good for big multi tier systems, but maybe to complicated for small projects For smaller projects the base version with added open source plugins from eclipse are an interesting alternative.
Also included in this version is the new IBM Worklight Studio 6.0 to build mobile applications. The strange thing is that applications which are built with IBM Worklight Studio 6.0 can not be deployed to the i. You have to deploy them to a Windows or Unix Worklight server which can then access the db/2 on the i.
Rational Developer for i RPG and COBOL + Modernization Tools, EGL Edition v9.0
*Updated*You can find additional informations to the new versions on http://www-03.ibm.com/software/products/us/en/dev-ibm-i. or in the announcement. Das Informationcenter wurde ebenfalls bereits für die Version 9 aktualisert.
Unfortunatly up to now there is no Tial version of 9 available, but i have already contacted a sales representative of IBM when and where a Trial for this version will be available. *Updated* Eric Simpson has blogged about RDI and at the end of his post is a tutorial how to install the trial with the installation manager manually.