I love both Pythonista and play.js on iOS, and it'll be nice to have another option. The former two, though, run the code entirely on-device, but from the looks of it Replit will run code on their servers? While that's not a surprise (given repl.it's model), it's definitely a little less useful for me (personally) since it'll require a persistent internet connection to test anything, and the code won't have access to anything on your device (as far as I can tell?).

I happen to really like the way play.js lets you run a full-blown Node.js server on your iPhone with access to native socket APIs (torrent client! on your non-jailbroken iPhone!), and the way Pythonista lets you access iOS native APIs via ctypes.