The Turris Omnia is an open, powerful router that comes with OpenWRT.
Turris adds an additional UI and features beyond that, but the OpenWRT UI is still available and the stock firmware can be completely replaced with OpenWRT if so desired.
It's a bit pricey but has great specs (1.6 GHz dual core, 2GB RAM, 8GB eMMC) and is an excellent device for tinkerers with headers exposing UART, JTAG, GPIO, and more. It has three internal mPCIe ports as well.
I am not affiliated with Turris but just happened to stumble upon a new one at a garage sale a couple of days ago. Lucky find and I'm excited.
Macklemore