I was watching the Modern Marvelsepisode about hand tools. It showed a hammer made by Stanley that had a tuning fork built into the handle to help absorb the energy of the hammer blow so that the vibrations would not be transferred to the user’s arm. The last time I saw an actual tuning fork in person was in my high school science lab.
Are they still used to tune pianos? Were they used to tune anything else?
I use a tuning fork to tune my classical guitar. It’s handy, highly portable, and more elegant than an electronic tuner or pitch pipe. I think it works great, but you have to have a good ear, of course.
The dude who tuned the piano at my school used them.
I’m sure a tonedeaf (or completely deaf) person could get away with a very sensitive microphone and an osciloscope, though. 
I’m not a piano tuner, but yes they are still occasionaly used to tune instruments (probably not instruments that need to be tuned by professionals tho), but these days most people have electronic tuners which have the advantage of being able to tell you how much you are off by and also don’t rely on the ear of the tuner.
Quite frankly an electronic keyboard is just as good as a set of tuning forks when tuning instruments.
Sure, they are, although there are now lots of electronic equivalents such as tuning meters for those of us with tinnier ears.
A tuning fork, pitchpipe or other “standard” is still an easy and portable way to produce a reference pitch. And yes, tuning forks can be used to tune other instruments besides pianos. I have used one to tune guitars and an autoharp, and I even saw someone use one once while tuning a pipe organ! 
Shoulda added this to the OP:
How do you use a tuning fork? I know you strike the fork to make it vibrate, but then what?
They’re used to tune pretty much any instrument, and they can also be used to effectively train the voice.
These days, most find it much easier to use electronic tuners for their instruments.
You strike the fork, that then gives you the correct tone. You then adjust your instrument so that the tone it plays is the same as the one given out by the fork.
Using a tuning fork requires a decent ear. Nowadays, many people use an electronic device where the note A can be set anywhere.
I know I’m gonna get heat for this, but… A is “Typically” set at 440. So, you can set the device to give you an A note that is resonating at 440 times a second, or at A-441, A-338, whatever you want to.
You can usually attach a device to a violin/guitar/necked instrument. I’ve seen those used. I do not know how one works one for woodwind or brass. I’d hope you can attach, and tune in a similar manner.
This AutoTuner Site shows quite a few of these devices for sale, with brief descriptions of them.
I hope this helps.
Cartooniverse
The tuning fork is designed to vibrate on a specific note. You then adjust that note on the instrument until it sounds exactly like the tuning fork. You then adjust the other notes relative to that one (or I suppose you could use lots of tuning forks, one for each note. But I don’t think I’ve ever seen it done that way.)
After striking the fork, it resonates with the sound of a certain pitch.
For example, if you had a fork with the pitch of C you strike the fork and then tune your instrument until the note you expect to be C matches the fork’s pitch.
There are forks for every pitch, but an electronic tuner is far more convenient than having 12 different forks.
Cartooniverse with woodwind and brass tuning meters are hand held devices.