How is EFS-Web different from PASAT and EFS-ABX?

Unlike USPTO’s original electronic filing tool, PASAT, and its follow on, ABX, EFS-Web is not a patent application authoring tool, but simply a means allowing you to easily and quickly submit patent applications and related documents electronically as PDF attachments. You choose the tool, process and workflow with which you author your documents; the only requirement is that prior to submitting them via EFS-Web, you first convert them to PDF files.

USPTO FAQ - Questions and Answers (31AUG2006)