I followed these fine articles [1] [2] to build my own router running Linux on a mini PC.

[1] https://arstechnica.com/gadgets/2016/01/numbers-dont-lie-its...

[2] https://arstechnica.com/gadgets/2016/04/the-ars-guide-to-bui...

The WiFi card in my mini PC turned out not to support access point mode, so I use separate WiFi routers as my access points. I could've replaced the WiFi card and run an access point on the mini PC too, but didn't bother because I needed multiple access points anyway to cover my house.

There's no fancy GUI to mange my router though, everything is done on the command line.