Stash for Reddit was an ambitious idea I worked on my spare time. Stash offered the ability to browse reddit without spending mobile data. Content (posts, images and videos) would be preloaded to the end user's phone provided it was connected to a wifi network, so that later on they could browse their favourite subreddits without messing with their data allowance.
The app attracted 20k+ users in a matter of days as it pioneered the "Early Access" category of Play Store (which was a new thing back in ~2017), with lots of good feedback.
Unfortunately it got shut down about half an year later. Downloading videos from YouTube is against their T&Cs, and without the ability to preload videos the app had lost its unique value proposition.
It was an overall good ride :).