An Intel NUC is a perfect device to use as a pfSense firewall. Here’s why.
- Low power
- Very small – smaller than most modems / routers!
- Can be expensive
- Cheaper models come with Realtek ethernet chipsets, the i3 model comes with Intel chipsets which will work.
- Only one Ethernet port
To work around the single ethernet port you can use a USB to ethernet adapter. Apple’s official adapter does work but these are expensive. However I purchased one off ebay for $9.89 delivered containing the AX88772A (ax88179_178A) chipset – said to be the same that is used in the Apple adapter (and admittedly the adapter does look very similar) which does work.
Update: It might also be possible to purchase the cheapest Intel NUC (currently $195) with DDR3L Ram (~$30) and 2 of the USB ethernet adapters ($20) which will give you a fully featured powerful router for $250. The only downside being the potentially limited rate of the USB ethernet adapters, but for ADSL connections this should be fine.
Update 2: pfSense have now released a tiny firewall appliance with dual NICs which is a much better solution than any of the above, if you are just a small office. https://netgate.com/products/sg-1000.html