Knocker is a simple and easy-to-use TCP security port scanner written in C. It is able to analyze hosts and the network services which are running on them. Knocker it is available for Linux and Unix platforms. Both a console version and a GTK+ version are available.
You can download it from the following link: https://packetstormsecurity.com/files/download/25603/knocker-0.5.0.tar.gz
Source: https://packetstormsecurity.com/files/25603/knocker-0.5.0.tar.gz.html