OPNsense 19" rack mountable appliance
all OPNsense appliances come with the e-book:
'pfSense The Definitive Guide' for FREE!

The OPNsense rack edition is an out-off-the-box firewall experience, with the pfSense open source firewall software in an embedded, fan-less appliance that consumes less than 5Watt, with all the features you might expect from commercial firewall solutions for a fraction of the cost.