Topsy partnered with Twitter to maintain an index of tweets going back to 2006. However, the company also made products to search and analyze social networks. It's likely Apple has used Topsy's talent and technology to imbue its products with enhanced search features. iOS 9, for example, debuted a new Proactive feature that uses data from Siri, Calendar, third-party apps and more to deliver more relevant search results to users.
On the market for an iPhone? Here's a breakdown of all the currently shipping iPhones from Apple.