Although this is under "Computer:display", the nature of the idea is such that it only fits here as well as it would in various other places, but it fits about as badly here as elsewhere too.
Take a random device, e.g. a laptop. It has speakers, a keyboard, a little wiggly thing wherewith you can
move a cursor, a display and so forth. Sometimes, one of these either stops working properly or just isn't very good compared to something else to which you might have access. In extreme cases, this can even mean you just lose the ability to use the device at all, at which point They expect you to go out and buy a new one, but since you are mainly dumpster-diving for goosnargh, maybe due to the recession and the decline of Western civilisation, that ain't gonna happen, so hmm, questionably optimistic business plan there i think, but we shall see. I'm an early adopter in that respect of course.
Anyway, with probably quite a lot of extra electronic jiggery-pockery which will presumably drive up the prices, why not make as many things as possible plug into as many other things as possible? So i've got a DAB radio on my left but am currently listening to yer actual radio on the crappy speakers of this mini-tablet due to crackly charging and reading my words on its display even though the radio display can show the few words i need for to cunnen type this. In the meantime the keyboard is on the blink even though there are several other devices in this room (e.g. a synth) with perfectly good keyboards.
So, the following devices could be made to plug into each other in meaningful ways in the following categories:
Speakers (and microphones) on radios, TVs, telephones, Hi-fis and in other devices such as media players, computers and consoles.
Displays on tablets, laptops, TVs, portable DVD players, radios and calculatrices, including seven-segment ones and blinkenlights.
Keyboards on typewriters, tablets, laptops, desktops, smartphones (including on-screen keyboards in that).
Pointing devices as in mice, digitising tablets, tablet tablets, the doobries on laptops, the little wiggly things on laptops, joysticks, sadnesssticks, games console thingies, touchscreens.
Storage devices including memory sticks, record turntables, eight-tracks, punchcards, reel-to-reel tape, VCRs, tape- and DVD-based camcorders, optical drives in anything with an optical drive.
Anything light sensitive, e.g. camera obscura rooms, scanners, pinhole cameras, cine cameras, instamatic cameras, cameras on 'phones, tablets, webcams, DSLRs and so on.
Printers, photocopiers, fax machines and all that lot, which put stuff on paper.
Probably some other things such as mobiles, fax modems and short wave radios, forming a sort of comms category and some other categories i haven't thought of like smoke alarms.
Also, undertake two projects: make a box into which you can plug any number of almost-compatible devices to make them compatible, such as an old camcorder with composite video output and a USB into which you'd plug a webcam (and write an appropriate driver presumably); and make a whole set of new devices which enable you to take something like a nineteenth-century still camera and use it in the same way, use an old film projector as a display device and a virginal to send SMS messages.
So yeah, basically plug everything into everything else.