In addition to Doug Lea's collections library, the Generic
Collection Library for Java (JGL) from ObjectSpace was an
early collection library available for the Java platform.
(If you are curious of how the library name
maps to the acronym, it doesn't. The name of the first version of
the library infringed on Sun's Java trademark. ObjectSpace
changed the name, but the original acronym stuck.)
Following the design patterns of the Standard Template Library
(STL) for C++, the library provides algorithmic support, in
addition to a data structure library. While the JGL is a good
alternative collection framework, it didn't meet the design
goals of the Collections Framework team: "The main
design goal was to produce an API that was reasonably small, both
in size and, more importantly, in conceptual weight."
With that in mind, the team came up with the Collections
Framework.
While not adopted by Sun Microsystems, the JGL has been
included with many IDE tools. Due to its early availability, the
JGL is available to well over 100,000 developers.
For a comparison of JGL versus the Collections Framework, see The
battle of the container frameworks: which should you use?
article in JavaWorld.