SynScan is a fast half-open port scanner. This tool will send TCP packets with the SYN flag to any block of destination addresses at very high speed. SynScan endeavors to send traffic as fast as the host network interface can support.
You can download it from the following link: https://packetstormsecurity.com/files/download/62221/synscan-5.0.tar.gz
Source: https://packetstormsecurity.com/files/62221/synscan-5.0.tar.gz.html