PRTG Traffic Grapher enables you to log and monitor data flowing in and out of any SNMP enabled network device, like routers, switches, firewalls and others. It provides a graphical interface with real-time charts and long term statistical reports covering daily and monthly periods. It also provides an option to generate interactive HTML reports. The version you are downloading is a featured limited, free version, that can be used with up to 3 devices. It has some features disabled and a nag screen, but does not expire. The trial of the commercial version requires you to submit your email address.