The OpenEdge Developer's Kit | Classroom Edition is available from Release 11.6.0 and does not provide access to any previous versions. But more experienced developers will commonly come across other versions of OpenEdge and need to work with those and need appropriate support. They may have development tools for those previous versions, purchased as perpetual licenses or as part of a subscription.
To understand what is currently available, what is supported and what has been retired, developers should consult the latest Product and Platform Availability Guides (PAGs) Wiki page which is located in the OpenEdge General group here on Progress Community.
PAGs reflect the current commercial releases for Progress products. These documents do not address plans for future product certifications and support -- they describe current support for the indicated products. This information changes on a regular basis so the documents are subject to change without notice.
The Product Lifecycle Guide is also available from this page. The Product Life Cycle Guide outlines the product development and technical support resources available during a product's life span. This document details the different product stages starting from the First Commercial Shipment (FCS) of the product to eventual product retirement, and provides the life cycle status for each Progress Software product. This information is designed to help you develop your product plans within the context of Progress Software's product life cycle plans.
Here is a sample, but you will find the latest on the OpenEdge General Wiki.