/usr/ports/net-mgmt/mrtg-ping-probe/
mrtg-ping-probe is a ping probe for MRTG 2.x.  It is used to monitor
the round trip time and packet loss to networked devices.  MRTG uses
its output to generate graphs visualizing minimum and maximum round
trip times or packet loss.

/usr/ports/net-mgmt/smokeping
SmokePing is a latency logging and graphing system. It consists of a
daemon process which organizes the latency measurements and a CGI
which presents the graphs.