I remember a few years ago when Yik Yak was at its peak popularity, some other app came along with the exact same formula with anonymous local feeds but will pictures instead of text posts. I heard about it from a friend because they were doing a promo to gain popularity where whoever had the most points on our campus would win $150. I quickly realized that I could just post a bunch of pictures then on a different phone go in and upvote all my pictures and down vote everyone else's, then delete then reinstall the app and do it all again. I spent about an hour doing this and instantly had the most points on campus by about 3 or 4 times what the number 2 person had. I did actually end up winning the $150 as then send me a message and sent it to me through PayPal. After the promo ended they put out a patch the fixed the ability to reinstall and upvote again. I uninstalled it after that and don't remember what it was even called or if it still exists. My friend was pissed when I told him later how I won.