iOS: If you've ever seen an interesting landmark or building and wanted to learn more about it, Curiosity is perfect for you. The app uses geolocation to float Wikipedia articles based on what's near you, and suggests articles related to trending topics in the news, so you stay informed, too. Curiosity's primary source is Wikipedia, so keep that in mind while you read, but for that, it's great at giving you the right articles when you need them. You can browse a map -- centred on where you are -- and see articles related to landmarks all around you. Tap one to read it, or bookmark or share it to read later. It's ideal if you're wandering a foreign city, or you're just curious about what's interesting in your own neighbourhood. It's not all factual, dry, reference stuff either -- the app will show you movies filmed or set in your neighbourhood, historic battles that took place nearby, and more.
If you're curious about the news, or you see people talking about a topic on social media but don't know the background, Curiosity can also float articles based on trending topics. If you want to try it out, it will set you back $2.99 at the iTunes App Store.