The major differences being that P/NaCL was: 1. An open standard/implementation 2. Used regular OSS code 3. Was actually written to be secure

The effort spurred ASM.js & eventually the WebAssembly standard because of the discomfort of deploying a cutting edge research to billions of people on the web (the initial NaCL implementation was very large & eventually turned out to have security holes, the original research was improved upon but by then the industry had spoken).

12 years ago, even.

https://en.m.wikipedia.org/wiki/Gears_(software)

Isn't NaCl deprecated now?