This thread is about some things I've discovered for people that want to play music in other than "modern tuning".
My threads 17 Tone Just Intonation Guitar and Removeable Fingerboards deal with the ancient just intonation tunings I have recovered and what a pain it is to find instruments that can play them. The frets on modern guitars are set to equal temperament tuning and have to be ripped out to change this. (I still haven't got my wide neck just intonation guitar worked out.) I talked with a music store owner and they told me you have to pay over five digits to get a keyboard that can be tuned each note individually. I bought a digital piano several years back and it won't let you tune the notes as you please so I had to use software to override it. I have given up using digital music so I am now only interested in analog instruments.
One thing I found is the old school analog "combo organs" of the 60s and 70s, such as the Doors used, such as the Vox Continental, a lot of them were tunable. You could set the 12 pitches as you like for the far right octave and all the other octaves would automatically be tuned accordingly, all pure 2 to 1 octaves. I'm trying to find out if any had double keyboards where you can tune them separately. That would allow me to play the ancient 24 tone just intonation tuning that I believe was used on double register harpsichords and organs.
Last year I bought a piano tuning hammer and kit from Howard Piano industries after watching their youtube vid on how to tune a piano and had a go at the old piano here. For me there's definitely a learning curve I need to get past. Pianos are very very poorly designed as far as tuning goes. For such an expensive instrument I'm sure they could use a system where you turn the pins with a ratchet and click things into place just how you like. I'm going to retry it sometime but it was not easy for me. Side note: The owner of a music store once told me if the metal tuning pins on your piano wear out the wood they sit in, the piano is only good for firewood. But I found online people saying you can breath life back into an old piano with loose pins buy using CA glue (superglue). If it's an upright you set it on its back and drop the glue around the pins and let it dry. They cause the wood around the pin to swell and this tightens the hold. Pianos of course can be tuned to alternative tunings, if you can do it yourself or afford to pay someone. I had to talk to four different tuners to find one that would do the ancient just intonation tuning I use. That was a couple years ago. I remember later that day, alone in the house, I let out a howl sitting at the computer here, and was startled by a sound coming from the piano. The 200 plus strings were so in synch with each other that they picked up the sound and the thing was humming, loud. It was awesome.
Ok so old school analog combo organs and pianos can be tuned as you like. Of course fretless instruments can be used to play alternative tunings as well. The amazing instrument the viola da gamba (the real precursor of the modern electric guitar) has movable frets. And there are references in Renaissance times to using 'testini", a fretlet of gut string glued to the fingerboard, to get precise notes on the viola da gamba. But I think there was an earlier way that used triangular beads the gut string frets went thru, with a bit of wax under the bead, to create raised areas on the frets for precise notes. Sitars have movable frets...
So I'm pushing on with my ancient just intonation analog musical project. There's one loose end. I work with the four just tunings I have recovered, 12 17 19 and 24 tone. I think it's possible in the ancient world they each corresponded with a particular season. So you would retune your viola da gamba (or whatever you called it then) with each change of season. But I'm not sure about this. Pushing on.