Graffiti is a free utility that lets you enter text on an Android phone using your own handwriting.
The app is based on the old Graffiti tool adopted by Palm devices several years ago, in the days before on-screen touch keyboards. Graffiti lets you write letters using your finger on a black slate that appears underneath the text editor, browser, mail client, etc.
The problem with Graffiti is that letters need to be drawn in a very specific way and all of these gestures need to be learned. There is a guide within the program, but it still requires lots of practice to be able to write words quickly. Letters are entered on the left-side of the slate, and numbers on the right. Graffiti includes separate gestures for accessing special characters and punctuation.
Even if you have the patience to learn the gestures and practice, you'll probably find it difficult to type faster than you can using the Android keyboard. If you really want to speed up your text entry then I suggest you download SwiftKey instead.
If you had a Palm back in the day, you'll have fun using Graffiti on your Android. However, the program looks very old fashioned compared with modern touch keyboards.