You can use normal WiFi Access Point routers for this.
The one I use is the Foscam N300. It works great for both ends of this application.
Just don't use the WAN ports unless you also intend to create a subnet.
-- Unless it has built-in bridging that actually works. I have tried several brands that claim to work but in practice they get confused.
If it doesn't have bridging, or if it doesn't work, then set it up as a normal AP and just plug into a LAN port on them, which is always internally bridged to its WiFi.
The router will think it has no WAN, but it should work for you.
If you use DHCP, make sure there is only one DHCP server on the entire subnet.
Or, as I do, just shut them all off and use static IPs, with the gateway address set to the closest router to the ISP.