XSS Online is described as 'Test for the XSS Online , Powerful payloads in the backend' and is a Vulnerability Scanner in the Network & Admin category. There are six alternatives to XSS Online for a variety of platforms, including Windows, Linux, Mac, Online / Web-based and Android. The best alternative is OWASP Zed Attack Proxy (ZAP), which is both free and Open Source. Other great apps like XSS Online are Burp Suite (Freemium), Nessus (Paid), Nikto (Free, Open Source) and Acunetix (Paid).
The Nessus vulnerability scanner is the world-leader in active scanners, featuring high-speed discovery, configuration auditing, asset profiling, sensitive data discovery and vulnerability analysis of your security posture.
Nikto is an Open Source (GPL) web server scanner which performs comprehensive tests against web servers for multiple items, including over 6400 potentially dangerous files/CGIs, checks for outdated versions of over 1000 servers, and version specific problems on over 270 servers.