Swype familiarized Android users with its gesture-style typing UI but it's pretty safe to say that SwiftKey, a keyboard replacement app and the best-selling paid-for program in the Google Play store, has just about perfected it.

Now in its fourth version, SwiftKey offers a "flow through space" feature that allows you to fly through sentences, gliding over the space key between words instead of lifting your finger from the touchscreen. Its predictions can also work with Flow — just lift your finger if the prediction is right.

But SwiftKey's appeal lies mainly in its word prediction capability, which can pull information from your text messages, GMail account and social media networks to match itself to your typing style, offering letters and even words with eerie accuracy. New users will probably need some time to get used to the interface, and it will, in turn, become noticeably better at predictions the more you use it.

One perk many reviewers touted was the ability to type by tapping in conjunction with gestures, which Swype does not. Its SmartSpace function also tells you when you miss the space bar, and will automatically correct your sentence. Another useful tool, which can help improve the efficiency of your typing, keeps track of statistics such as typing accuracy, number of keystrokes saved and the letters on which you typo most frequently.

The app works in dozens of different languages, and can enable up to three simultaneously. The tablet and smartphone versions are largely the same, but on tablets in landscape mode the keyboard splits, placing number keys in the center and allowing your thumbs to more easily reach the letters.

The keyboard itself is also customizable, with options to change the color scheme and even adjust key height for your typing style.

At $1.99 for smartphones and $3.99 for tablets, it seems somewhat pricey, but well worth the price. SwiftKey has made itself so indispensable to so many thousands of users that it even has an Xkdc comic.