CAT

CAT is designed to facilitate manual web application penetration testing for more complex, demanding application testing tasks. It removes some of the more repetitive elements of the testing process, allowing the tester to focus on individual applications, thus enabling them to conduct a much more thorough test. Conceptually it is similar to other proxies available both commercially and open source, but CAT provides a richer feature set and greater performance, combined with a more intuitive user interface.
There are a number of differences between CAT and currently available web proxies. They include:

• CAT uses Internet Explorer’s rendering engine for accurate HTML representation
• It supports many different types of text conversions including: URL, Base64, Hex, Unicode, HTML/XML, SQL and JavaScript no quotes
• It offers integrated SQL Injection and XSS Detection
• Synchronised Proxies for Authentication and Authorisation checking
• Faster performance due to HTTP connection caching
• SSL Version and Cipher checker using OpenSSL
• Greater flexibility for importing/exporting logs and saving projects
• Tabbed Interface allows for multiple tools at once e.g. multiple repeaters & different logs
• The ability to repeat and modify a sequence of requests (particularly useful in SSO testing)
• It’s free!

Do bear in mind that this is a free tool, but it is NOT Open Source. Also take a good look at the EULA before using it (especially Section 6).
You can download CAT Beta 4 here:
CAT_Beta_4.msi