I run a bot that posts Street Art pictures from Instagram [1]. The bot dominates the hashtag search term results [2]. People who find the bot, click the profile and click the URL associated with an app I made for discovering street art [3].
The bot dominates search results because it finds hashtag heavy images via Instagram. The hashtags on the Instagram image carry over to the Twitter post, resulting in an active searchable Twitter feed. The bot posts a over a thousand times a day.
Since releasing the app, I've averaged about 500 downloads per month, without any promotion. It works very well for consistent passive traffic.
[1]: Bot http://twitter.com/publicartfound
[2]: Search term https://twitter.com/search?q=streetart
[3]: Landing page http://publicart.io