BApp details: Sentinel
This extension can be used to help test for certain categories of vulnerabilities, including XSS and SQL injection.
To use, select an HTTP request, and choose "Send to Sentinel" from the context menu. Sentinel will then issue various requests, with attack patterns inserted. It will analyze the resulting HTTP responses to try to find vulnerabilities.
You can install BApps directly within Burp, via the BApp Store feature in the Burp Extender tool. You can also download them from here, for offline installation into Burp.
Please note that extensions are written by third party users of Burp, and PortSwigger Web Security makes no warranty about their quality or usefulness for any particular purpose.