im on android and i use poweramp, Shit is sooooo good! you can set the amount of crossfade between tracks!
@ the original question, sounds you want to play multi tracks withOUT gaps? If yes, i agree with the post above. @astreme, i didn't know you could apply cross fade, i will have to youtube the How To video, thanks for the tip.
its free on apple stock music app, they want to make foldable phones when they cant even do the basics