Burp Repeater is a simple tool for manually manipulating and reissuing individual HTTP requests, and analyzing the application's responses. You can send a request to Repeater from anywhere within Burp, modify the request and issue it over and over.
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Burp Suite Free Edition v1.6 contains significant new features added since v1.5, including support for WebSockets messages, PKCS#11 client SSL certificates contained in smart cards and physical tokens, a new Extender tool, allowing dynamic loading and unloading of multiple extensions, and the BApp Store, allowing quick and easy installation of extensions written by other Burp users.
Burp Suite Professional contains a number of bugfixes and tweaks, added since the last beta version.