The Animal Sniffer Plugin is used to build signatures of APIs and to check your classes against previously generated signatures. This plugin is called animal sniffer because the principal signatures that are used are those of the Java Runtime, and since Sun traditionally names the different versions of its Java Runtimes after different animals, the plugin that detects what Java Runtime your code requires was called "Animal Sniffer".
WizTools.org RESTClient is a Java Swing application for testing RESTful web services. It might be used for testing other HTTP communications too. This is a short introduction of this tool explaining its various features.