Alien Blue is the most popular Reddit app for iPhone and iPad, developed by Jase Morrissey and acquired by Reddit in October 2014. The universal iOS app is free on the App Store, and a Pro tier was previously offered as a $1.99 in-app purchase.
However, Reddit has since decided to focus its efforts on developing an official Reddit for iOS app, and Alien Blue will be removed from the App Store once the new app is released. Reddit for iOS is currently in closed beta testing.
Alien Blue will remain accessible by users that already downloaded the app, but Pro features will likely require a Gold subscription going forward. Reddit's free four-year Gold subscription should help bridge the transition for existing Pro users.
Reddit Gold is a membership program that provides perks such as turning off ads, custom themes, custom avatars, new comment highlighting, subreddit filtering, saved posts and comments categorization, and more. Reddit Gold is $3.99/month or $29.99/year.
Alien Blue [Direct Link] remains available for free on the App Store in the short term.