Pfsense/opnsense would be one option (based on FreeBSD). For Linux there is OpenWRT, which you can either run as an alternative firmware on quite a few consumer routers/access points, or install on a PC or Pi or similar.

Caveat: I have only used OpenWRT on a high end consumer router (GL.inet MT6000) out of those. That works well, anything else is based on reading about people using those options.

For all of those, once you set it up you don't really need to do much except install updates a couple of times per year, or if you want to forward a new port or such.