Nmap has established itself as a premier, free, open-source network mapping tool. There are alternatives that are also free, though they vary in their sophistication and ease of use.

nmap 192.168.1.0/24 will scan the entire range of 254 possible IP addresses on my local network and let me know which are pingable, along with which ports are open. If you've just plugged in a new ...

Nmap doesn't perform vulnerability assessment; it's only a port scanner. If something more sophisticated is needed to spot flaws, consider using an automated Nessus-based approach instead.