Excellent synth SunVox (it’s older version):
The open source album in SunVox:
Nimsynth:
DCubix Twist:
Loudmax limiter: https://loudmax.blogspot.com/
It’s LADSPA version for Linux:
https://www.mediafire.com/file/mrbrtyhrq3ngn3w/LoudMax_v1_32_Linux_x86_LADSPA.tar.xz/file
I stopped off at Sunvox on my journey to Zynthian. It is pretty good. I got a bit frustrated with its use interface and some complexities in sound creation but he has poor a lot of effort into a fairly complete and flexible synth engine / environment.
Sunvox has nice tracker ideology, like Fasttracker loong before with it’s own limits but definately with lot’s of advantages. It’s cool when you get used to it a bit (have it on android smartphone, ipad pro) but - can’t create a fully grown piece on it. Whatever you do, it will have some tracker taste in it. So imho - not a good thing for zynthian, as it would take too much time to adapt to our sandbox. And what for, zynthian is a completely independent creature with it’s own unique features never discovered before, am i right ?
All what I personally need in the Zynthian for my full music work (ideally, not maybe doable at the moment, but I hope for the future), is an x-channel x-section (4, 6, 8, or maybe 16?) looper with quantization, undo/redo, and each channel volume, and with the final bouncing to the stereo output track, to make a whole music creation on the Z. Am I demanding too much? 
P.S.: As of today, I’ve tried ALL possible loopers for music work (Boss R-3, RC-202, RC-505, ENX 95000, OP-1 (tape), even the new 1010music Blackbox, Aeros loop station, even the last Organelle M). Only left for myself the RC-202 for awhile. Others were returned back, as nothing convinced me fully.
I use LoopyHD on iPad Pro for live looping - sufficient for me (as it is much more advanced than most of hardware loopers and with far better sound quality too).
But definately @sm7x7 you are not alone here in your desires . MIDI looper is also a long time wanted feature, so “Just you wait mr.Higgins, just you wait…”
The iPad with the looper soft (not just Loopy, but recently added apps like Quatiloop, OneLoop, LiveLooper by L7, or MIDI looper InfiniteLooper will be great solution for me IF the iPad (in my case iPad Mini 4) could be incased in proper audio dock like Alesis Dock or Behringer one… I do have Focusrite dock which somehow works for iPad Mini (and very buggy sometimes), but it’s not the portable solution - would like to have something battery powered… Well, I’m a fan of the All-In-One stuff, and the Zynthian for me is THE number 1 solution for now, and I’ll hold on tight until we’ll have mentioned above recording stuff on it
I have Quantiloop, InfiniteLooper too. But don’t use them so often (maybe got used to Loopy wich also has good multichannel card support). But other stuff like Samplr, Blocks Wave and Borderlands I use quiet a lot. As well as my favorite synth on apple platform - Magelan.
Completely agree that it’s not a portable stuff. Lightning to usb 3 adapter etc. - to unreliable, wires can break at any moment. Even tried to make some kind of case (like guitar pedal rig) with everything connected and you need just to plug output jack’s/ XLR to the system. Still, risky.
On the other hand, impressive live artists like Beardyman rely on a few iPads (even with completely rewritten custom software) for realtime gigs. It means, this stuff can be reliable enough…
But my vote is with Zynthian ! Let it evolve beyond our imagination 