I use Flym (Android). It’s not being developed anymore unfortunately but on the other hand it was left in a very good state and it’s perfectly usable with lots of good features. I especially like the built-in feed search, it’s very good and 9 out of 10 times it will find the feed you want and you can add it directly. Beats the hell out of poking around websites trying to find if they have a feed and where it might be.
It’s not the code as much as the infrastructure + testing that would not be realistic to put together in such a short time.
I’m curious in fact to see if Reddit can still manage their own r/place this time around, given the turnover and people who left.