I am happy to temporarily stop playing the Striso (upon which I get some hours a day; one would think I’d be better by now, but am an "old rookie) and share.
Here’s what I use (and admittedly, on the cheap, so no overwhelming hundred-dollar standalone instruments, or anything):
ThumbJam, and many of the free additional voices. While they don’t all “move” like some others, I use Tenor Sax, Concertina, Violin and Viola and Cello, Banjo, Cittern…you name it, and I probably use it. I use them as individual voices, but also as combinations with #s 2 and 3, below:
Roli 5D, which was free, but I bought a couple of 4 dollar 12-packs of instruments, so I’d get nice acoustic sounds like Duduk and Steel String Guitar and lots of orchestral sounds. These sound wonderful by themselves, and have quite a few options with adjusters at the top. More important to me is the abilitiy to “feed” them with ThumbJam sounds (without hassle or complications) so they get enriched, depending upon my choice. I like TJam Acoustic Guitar with Roli Steel String, for instance.
And here, it gets kind of nice in other ways: I use GeoShred, which comes with nice synth sounds of all sorts, and some good instruments, but the real sweet sounds, to my ear, come from some elegant add-ons of “acoustic model” instruments, from SWAM and Naada. SWAM winds I like: Clarinet, Oboe, Flute for favorites; and I bought 2 Naada instruments; Duduk and Erhu. The Duduk is nice, but only an octave and a half, and the Erhu is very cool. Each (and all Geo instruments) comes in 10 or more variants, so much to experiment with. Now, my favorite Geo instrument is the Oboe, which also has a limitted scale (maybe 2 octaves) so what I do for it and Duduk is to pick a compatible ThumbJam voice (Tenor Sax, usually) so that the notes above and below the Geo range still sound when I push, and the result is not very noticeable when I only get the ThumbJam note at top or bottom of a run or phrase.
I realize that when I add all the instruments I put in GeoShred, it is a hundred bucks. But ThumbJam was, like, 12 dollars and Roli free plus about 8 dollars worth of options. All told, still a relatively inexpensive hobby, at least compared to my concertinas!
I bet others will weigh in with (probably) completely different favorites, which is part of what’s so cool about Striso and all these new controllers. So far, I have only played them “in public” over JamKazam, Jamulus, and Sonobus platforms, and shared some quick samples in SoundTrap (which I forgot to mention, has many, many sounds/instruments, including some very nice ones, and lots of “DAW-like” options and easy remote sharing, though not real-time) but nobody has turned me (and those sounds) away from sessions. I don’t expect the same (not yet, anyway) from my local Irish Trad or Old Time sessions, but in time, I suspect my little Striso and iPad and small speaker will be at least as acceptable as, say, a Roland digital accordion. Those “look” acoustic, but certainly have more in common with Striso under the skin than with vibrating metal reeds, eh?
And, one more I forgot: My friend Aaron has used his with Surge, a free and open-source major synth for PCs, and more, and it sounded amazing, but my old laptop doesn’t like it so much, yet. I need to try harder with it, but it doesn’t work on my iPad so would not be portable, by my standards. So far, everything I would take out to play fits in a large shoebox, with lots of room to spare! I suppose “shoebox plus laptop” would still be portable, but the iPad has me hooked…odd that I don’t like Garage Band.