1T3XT offers a suite of products that are useful to create and/or manipulate documents, more specifically PDF and RTF documents. There's some support for XML and HTML, but this isn't the core business of iText.
This is an overview of the products that are made available by 1T3XT:
iText is the original (core) product. It offers different ways to create and manipulate PDF documents. Most of the information and examples featured on this site deals with iText. The book iText in Action covers all the functionality you need to get started with the product.
iTextSharp is a .NET part of iText maintained by Paulo Soares. The iTextSharp releases are kept in sync with the iText releases. iTextSharp is written in C#. There's also a J# port written and maintained by Kazuya Ujihara: iText.NET
iText RTF used to be distributed with the iText.jar, but the functionality was moved to a separate jar since iText 2.1. You can use this library to create and manipulate RTF documents. Some people say iText RTF can produce or manipulate Word documents, but this is a misconception. Although Microsoft Word can interpret documents in the Rich Text Format, there's a huge difference between RTF and the Word doc format.
The iText Toolbox combines a number of ready-to-use tools (such as "concatenate", "split", "burst", "add watermark",...) in a Graphical User Interface. This tool is aimed at a large audience.
iText RUPS is a graphical tool for Reading and Updating PDF Syntax. It allows you to visualize a PDF (using SUN's PDF Renderer) and at the same time look at the internal structure: the PDF object and PDF syntax that make up each page in the PDF document. This tool is aimed at an audience of PDF specialists.
