Short answer - an auto-switching AV switch, or a decent AV receiver can take multiple inputs and output them to one display. Depending on your needs, the answer is different.
While certainly not the best (I wanted to do it on the cheap but without losing any quality - I went through several smaller setups that were lacking before this one), I had success with a long chain of switches and cables going to only 3 inputs on my CRT TV (composite, S-video & component) without needing to do anything but turn the console on and switch to the correct video TV video source with the tv remote. IMO the video quality was not noticeably degraded despite the bulk of cables running hidden behind the entertainment center.
An old post with a picture of my old switches here:
Topic: RCA/S-video selector
I was using a SCART to YUV(Component) transcoder and was able to cram a few more consoles in after that post before I made the switch to an XRGB and Keene SCART Commander with a Logitech Harmony remote.
The hardware in my CRT setup involved
Two
Philips PH61150 chained together in auto-switch mode
Intec G5295
Unnamed non-powered 5-to-1 SCART connected to a
Cypress CSY-2100
The only expensive part was the Cypress transcoder, tho at the time it was the cheapest available option for getting SCART RGB onto my TV. The Philips switches were purchased for around $20 each at a liquidator and the heavy shielded component cables for around $5 each at the same place. It was perfect for my SD CRT and I'd recommend any but the Cypress transcoder (some nagging problems with certain systems from several people due to I think cabling and signal issues which other hardware can deal with better).
Some further reading on the previously linked post and this one too wouldn't hurt -
AV Switch
For my few consoles I use an old A/V Receiver. It was my Onkyo that was in the living room but then the HDMI pass-thru began to mess up. Tiny drop outs bare noticeable except that streaming apps using HDCP freak out thinking you're an irate pirate and you have to restart the stream. So it got retired. It's hooked up via S-video and composite to a 27" Sony TV. Only 5 or 6 inputs (not counting composite from the front) but it works. The same cable does double duty for GameCube and N64 (swap it at the console). Signal looks nicer than the switches provide. My sound goes through some rather old JBL book-case speakers. Left, center and right. 
