Mapper is a network connectivity tester that employs a number of techniques to try and guess if a host is alive or not. Since many machines have ICMP firewalled off, it uses 7 different TCP and ICMP tests in attempting to gain some sort of response. Mapper can send spoofed decoys and use random delays for added stealth.
You can download it from the following link: https://packetstormsecurity.com/files/download/30034/mapper-2.19.tar.gz
Source: https://packetstormsecurity.com/files/30034/mapper-2.19.tar.gz.html