fping — Ping Many Hosts at Once
fping probes many hosts in parallel rather than waiting for each in turn, so checking a subnet takes about as long as checking a single address. It reports which hosts responded and which did not, in a form meant for scripting rather than reading.
Why run it
The use case is inventory rather than diagnosis. After a network change, confirming that everything which was reachable still is; after an outage, establishing the blast radius quickly; on an unfamiliar network, finding out what is actually on it. Sequential pinging makes these impractical at any real scale — a /24 checked one host at a time is several minutes of waiting, which is enough friction that people skip the check.
Why automate it
A sweep is a snapshot, and its value multiplies when you can compare snapshots. Scheduled sweeps tell you when a host that was always there stops responding, and equally when something new appears on a network where nothing new should. Neither is visible from a single run, because a single run has nothing to be different from. This is also the natural way to keep an inventory honest, since the alternative — a document someone updates by hand — is always wrong.
What it gives you
Fast, wide reachability checking that makes "verify everything still responds" a routine step instead of an afternoon. Run on a schedule it quietly maintains an inventory nobody has to update.