Spreed uses a technique called rapid serial visual presentation, or RSVP, to help you read text faster. By presenting text this way, you reduce sub-vocalization ("sounding the words" out), unconcious re-reading, and eliminate eye movements, which are the main things holding back your reading speed.
Every time we look at something, our eyes focus on a small area within our vision. Increase the number words your eyes can focus on, and thus read, per glance to further accelerate your reading speed.
Spreed tracks how much faster you're reading, and how much time have you've saved while using Spreed. How much more productive could you be if you could read 2-3x faster?