These distributions are all available for download from http://sourceforge.net/projects/dita-ot.
Full package distribution
To process DITA documents you must also download and install the Java J2SE SDK.
If one of your target output types is HTML Help, you will probably want to install the Microsoft HTML Help compiler. If you one of your target output types is JavaHelp, you will probably want to install the JavaHelp processor.
Small package distribution
The small package distribution contains only DITA Open Toolkit. You must separately install all the other required and optional processors to create a functioning build environment.
Release 1.2.2 and prior releases of the Toolkit were distributed only in this way.
You might want to download this distribution if you have a prior version of the Toolkit already installed, since the release 1.3 and 1.3.1 Toolkit prerequisites are still the same as those for release 1.2.2.
The small distribution is typically the one used to embed the Toolkit in other products.
The source distribution contains the source and executable code for the Toolkit (and it also contains the source code for this document). You might download this distribution if you need to modify Toolkit Java code or if you want a detailed look at how the Toolkit works.