Another keyboard based on extensions, or slashes, is Slash Keyboard. It has built-in search for Google, Giphy, emoji, Google Maps, YouTube, Amazon, Spotify, Facebook, Twitter, SoundCloud and many more services.

Hit the Slash button to the left of the space bar to immediately begin searching something like Product Hunt. Tapping on one of the search results will automatically paste it in the text field you're typing in.

Slash Keyboard is entirely free, and it's very unique. I've always called it the Swiss Army Knife of software keyboards. However, it lacks the strong autocorrect of other keyboards, as well as gesture typing, which can make it a pain to use at times.