BlueJ vs Eclipse
A free Java Development Environment designed for beginners, used by millions worldwide. BlueJ has a deliberately smaller and simpler interface than professional environments like NetBeans or Eclipse. This allows beginners to get started more quickly, and without being overwhelmed.
Eclipse is probably best known as a Java IDE, but it is more: it is an IDE framework, a tools framework, an open source project, a community, an eco-system, and a foundation.