Slide is an open-source, ad-free Reddit browser for Android.
Googling "open source reddit app" nets this: https://github.com/Haptic-Apps/Slide
NOTE: The number of mentions on this list indicates mentions on common posts plus user suggested alternatives. Hence, a higher number means a more popular project.
1 project | reddit.com/r/zen | 28 Jun 2022
1 project | reddit.com/r/slideforreddit | 13 Jun 2022
FOSS reddit app?
1 project | reddit.com/r/fossdroid | 30 Apr 2022
1 project | reddit.com/r/ProgrammerHumor | 27 Apr 2022
Does anyone know what happened to the dev?
1 project | reddit.com/r/slideforreddit | 22 Apr 2022