The custom “community build” firmware for Hyperkin’s Retron77 has just been updated. This version increases compatibility, however some games still need to be played via a ROM. For a detailed list of updates, as well as a full list of features, check out the post and first page of the topic on AtariAge:
http://atariage.com/forums/topic/281462-retron-77-community-build-image/page-7#entry4168162
https://www.dropbox.com/s/q2965rrzpo0jq2e/sdcard.remo.20181120-1353CB.zip?dl=0