UPDATE: Day 1 apps are now live. You can check the whole list at this link.
Google in a blog post confirmed its Play Store has officially crossed 25 billion app installs. To celebrate this significant milestone, Google will discount select apps and games to 25 cents over the period of next five days. In addition to that, Google will also offer special collections like 25 movies, 25 music albums and songs, 25 books etc. at discounted prices.
The discounted apps will be revealed later today.