We are occasionally asked what sort of affordable x86 equipment is good to run OpenWrt on. Here are a few options we think are worth considering:

1. A tiny PC with dual Ethernet sockets (Intel NUC and clones, Zotac Zbox, etc.) This will be router only and will require a switch and/or access point to make the network functional. Note that if a tiny PC has a wireless network card, it is probably a client-mode-only card that cannot be used in an access point. However, it may be possible to replace it with a card that supports the access point (AP) mode, so that the tiny PC can have access point functionality.
2. An industrial PC. We are especially partial to Lanner FW-74xx and FW-75xx models. They are a little bigger than a typical home router, about 10.5 x 5.5 x 1.5 in (27 x 14 x 4 cm), have distinctive ribbed tops for cooling, and can come with as many as six Ethernet ports, so you may be able to combine routing and switching in a single box. Wireless will still require a separate access point. When new, these things cost about seven metric tons of money (for a good reason: they are rugged and dependable), but occasionally, you can snag a used one for a reasonable price.
3. A quasi-industrial PC. These are usually not ruggedized per se, but borrow the industrial PC's aesthetics (ribbed cases) for the sake of passive cooling. There are some Chinese companies in this space that crank out decent product; look at Qotom and Vnopn (funny names, but in the age of search engine they are distinctive and thus easily findable). Depending on the model, you get anywhere between two and six Ethernet ports. As for built-in Wi-Fi, the tiny PC caveat applies here as well: the manufacturers usually install wireless cards that do not support the AP mode. On the luxury end of this space, there's Protectli; they have a range of passively cooled products with two, four, or six ports and processors that go up to Core i7.
4. A branch router. Depending on the model, you get between four and eight Ethernet ports and may or may not get built-in Wi-Fi. If you do get Wi-Fi, it may be an N card or an AC card.

One obvious name in the branch router space is Sophos; they have a range of boxes which periodically go out of support, so their corporate customers constantly upgrade to the new ones, and the fully functional old ones end up in the secondary market. Note, however, that Sophos has four product lines: RED, SG, UTM, and XG. RED boxes are not x86-compatible, so stay away from them. UTM boxes are actively cooled (although very quiet even when the fan is on); plus, they are no longer manufactured, although you can still find them in the secondary market. SG and XG, on the other hand, are passively cooled. Sophos distinguishes SG and XG because they ship with different software; hardware-wise, however, an SG105 is hard to tell apart from an XG105. Specific models we worked with include XG85(w), SG105(w), SG115(w), and SG125(w); the "w", if present. indicates wireless capability. Because of their deployment model, you can sometimes get amazing deals on these. These models usually come with Intel Atom of some kind (typically, E3xxx). RAM-wise, the older ones have a single 2 GB stick; newer ones may have a 4 GB one. Note the "stick"; it is standard PC memory, which may be upgraded if needed.

Somewhat less ubiquitous, but very similar, are Cyberoam CR products. In fact, they are so similar that in 2014, Sophos acquired Cyberoam. CR15iNG has three Ethernet ports, CR25iNG, four, CR35iNG, six; there are also sister models with wireless networking, CR15wiNG, CR25wiNG, and CR35wiNG. All these devices are actively cooled and built around AMD G-series processors, rather than Intel Atoms.

One other potential avenue to explore is an extensible thin client, but it is likely to require some handywork. HP has made a number of suitable models, usually with "Plus" in the name (HP T610 Plus, HP T620 Plus, etc.). There's also the Fujitsu Futro family, very common in Europe, less so in North America. These devices are built on low-power AMD processors and have a PCI extension slot on the motherboard. Sometimes, it us populated with an extension card (a DVI port, a pair of COM ports, or whatever else the wholesale buyer wanted), but more often, it is left vacant. Regardless, a two- or even four-port Ethernet card can be installed in the expansion slot, so the device can have routing capability (the pre-existing Ethernet port remains usable as well). The Wi-Fi card, if present, is almost guaranteed to be client-mode-only, so as is, the device can only be used as a wireless bridge. With an appropriate Wi-Fi card, however, the access point functionality is a definite possibility.

But in the final analysis, almost any PC derivative with more than one Ethernet port is a good candidate for OpenWrt deployment. We've had good results running OpenWrt in a small business setting on ancient 32-bit PC derivatives such as Blue Cat Adonis XMB2 or Check Point U-5, aka Lanner MB-7520.

If you feel like picking our brains on this or similar topic, feel free to contact us.