I happened to be reading about the Apple Newton and its handwriting recognition capability named Inkwell. Remembering that it was once a part of OS X, I searched for it. I found the following article that shows a history of OS X features and when they were introduced. Inkwell was introduced with Sherlock in OS X 10.2 Jaguar back in 2002, but the article indicates it was dropped.
Can it really be that long and when was it dropped? Another article indicated that it was still around in 2012. It also said that doesn’t show up unless a pen-based tablet is attached. I dug out my old (10 yrs?) Wacom Intuos GD tablet and attached it to my new Mac Mini running Yosemite. When opening System Preferences, a new extension name “Ink” had appeared. Unfortunately, the tablet didn’t work. I downloaded the latest driver from Wacom but it still didn’t work. The tablet works on my old Power Mac G5 running Tiger 10.4. From the Wacom legacy driver website, it looks like Wacom finally dropped support for this tablet after Snow Leopard 10.6
So if you have a newer tablet than I do, rest assured that the Inkwell handwriting recognition technology from the Newton is still available. Read the following articles for more info.