You can glue them together for double phones.

You can use it as a security camera on the cheap.

SyncThing backup storage.

If its not crazy old you could get a super cheap nvmo service and toss it in your car/emergency bag with a spare battery pack and cable

Leave one in the car, for emergencies

I don't know if it's still viable but few years back I used to use my old Android phone/phablet as extra monitor for my pc to monitor stats with Spacedesk. It runs on wifi and gives you the ability to add multi devices as monitors so potentially you can make all your old phones into many monitors for your pc as long as they are all on the same network.

https://www.spacedesk.net/

Home assistant + fully kiosk browser

(Or root + termux + docker)

Something I was looking at the other day: you can use them as Streamdecks. (StReam, not Steam.) Basically they become external keyboards, each key being assigned to a function such as start a program, select a tool or whatever, with a graphic to suit.

Elgato (who make the Streamdeck) make an Android app to use a phone as a deck, and there are several other such apps.

You could also have a look at r/androidafterlife

Turn them into sms gateways

r/androidafterlife is a good place to look

A wifi web cam is something i’ve been using an old Nexus phone I still have. The picture is pretty good and I like that I can out it anywhere there is wifi.

I used mine to monitor stats on my gaming PC with an app called Remote Systems Monitor. I think you have to pay a one time fee to unlock everything, but it was well worth it imo. The application on your PC sends the data to the app over your network locally.

I paired it with Automate app, so when my PC turned off the power to USB got cut, the phone would lock and dim the brightness down to 0 - just so I'm not frying the battery. Then it would do the opposite when I turned my PC back on, was a pretty fun little project to do.

bit of retro gaming? - https://www.youtube.com/watch?v=fTjZ84HjN2g

Set it up as a smart display with a dashboard of some sort and hang it up somewhere?

You could create an IP Webcam that could be used with a program like Frigate (I think that's what it called).

install moonlight and stream games from pc

Buy an Xbox controller with phone mount. Enjoy your steamdeck with geforce now.

Install DroidcamX and turn them into webcams or surveillance cams. It works over LAN and over USB. On LAN you can connect the phones to the server or the server to the phones, as you wish.

On Linux they're seen as regular V4L2 devices. You can use its custom kernel module (installs via DKMS) for additional customization options or the standard V4L2 kernel module.

I'm not really knowledgeable about recording and motion-detection (I've only used it as a webcam) but perhaps someone else can help with that.

Use it as a photo frame/ album

A lot of great ideas in this thread. Sadly, I don't have any spare phones that don't have a broken screen which is usually how they meet their demise. Just curious, how much of a concern is it to have the phone plugged in and charging all the time. A little bit worried about an exploding lithium ion battery.

Write an AI bot to do Hinge swiping for you

Maybe as a central display for your home assistant? As a dashboard or switch panel

I have an old LG phone, placed horizontally that I rest on a phone stand and use as my bedside alarm clock

One of my first Android phones... (a Motorolla Droid X) became our digital clock, years ago. This all happened because the cable TV box we had at the time didn't have a clock on it. We used it for a few years that way.

Line them up using a stiff support and take 3d photo’s.

Turn them into security cameras:

https://play.google.com/store/apps/details?id=com.ivuu&hl=en_GB&gl=US&pli=1

https://alfred.camera/

I have one in the door peephole. Using Android ip webcam I can turn it on to see through the screen who's behind. Also i added it to home assistant so I can see through it anytime. If someone rings turn the screen on, so you know who is it without getting too close. Send a photo to your smartphone when somebody rings...

Wifi based walkie talkies for the kids? hehe

Currently using 4 android phones I got from friends/families "junk drawer" to use as a home security system.