Read the title and came in to say… “weeeeell you might be interested in a Dirtywave M8!!” then read the rest of your post :D

My .02 OP-Z it has a specific sound but it’s great for sketchign ideas and the sequencer is pretty fun and can be pretty chaotic.

Norns seeems like it could be portable, but you would need a midi keyboard, powerbank etc. It can be pretty limiting by itself.

NTS-1 seems like a must buy if anything to have as an FX box but I don’t have one.

Not mentioned but “fits the bill” of portable stuff is the Circuit Series. I have a Circuit Tracks and it doesn’t get as much use as the M8, but it’s pretty fun wiht the pads to come up with different loops and ideas

A pack of Kastl 1.5 + Kastl Drums might be fun to hook up together.

I don’t know about the other stuff but the M8 is just mind blowingly great.

For portable versatile stuff like I think you’re looking for theres also the organelle, which seems awesome. Its another teensy based (I think?) beast that runs multiple Pure Data programs simultaneously. That means you can pretty much do anything.

The m8 though, it’s incredible. It’s such a full, polished product. It’s amazing how much power there is in that thing.

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Modal Skulpt is my go to mobile synth. Battery powered and comes from the factory with a lid to protect it. I’ve beaten the crap out of mine over the last few years and it never misses a beat. Even took it to 12,000 ft on a backpacking trip.

It’s the only piece of gear I own that I don’t worry about how I handle it. I’ll jump in the front seat of the car and toss it in the back seat over my shoulder. It was designed to be mobile rather than just a synth that’s small enough to be mobile.

You already mentioned Roland mini synths, but I think the SH-4D is worth calling out separately from the rest. Some of its oscillator models are based on vintage synths, sure, but not all. It doesn’t feel like just another rehash to me.

Probably too close to the M8 but Polyend Tracker Mini is a smaller version of the Tracker but more portable and battery powered.

I love all-in-one portable grooveboxes and I think the M8 is my favorite of the ones I own.

Ones I haven’t seen mentioned yet:

• Synthstrom Deluge - Extremely flexible powerhouse and a pleasure to use now that it has been updated from a 7-segment display to an OLED display. Not tiny, but is about the length/width of a laptop and is battery powered.
• Elektron Syntakt

I agree with @segfault that the Syntakt (and Digitakt) fit the bill very nicely. The first two weeks I owned the Syntakt, I spent the whole time exploring it from my couch.

I gotta say, while the S-1 is technically a “rehashed” SH-101, it’s a phenomenal device and I feel that description does it a slight disservice. Four voices means you can do some great pads, and the waveform chop function really pushes it into new territory.

The Modal CraftSynth 2 is in this category. I have one and I’d say I like it (but maybe not love it) - great for a class of digital wavetable sound no analog synth can match (but also does decent analog-ish subtractive synthesis). The SH101-style sequencer in the CraftSynth2 is a bit different to the usual, but in a fun way - works quite well for acid IMO.

The Korg NTS-1 is handy as long you are sequencing / playing it via an external controller - the ribbon keyboard on it isn’t useful. It’s versatile since it also makes a good effects unit (which is how I use it almost exclusively). There are a bunch of free and paid ‘plugins’ you can load onto it to expand the sound palette too, and even write your own using the open SDK if you are so inclined.

Deeper into DIY, Shruthi, Anushri, TSynth and (sadly unobtainium) Plinky probably fit on this list.