I wrote this HTML5 Across Lite reader over the course of a few weekends in 2011. According to the original announcement, this was the only way to render NY Times puzzles on Linux at the time. A build of this code has been running at http://derekslager.com/puz/ since that time. Since then, the NY Times has added a first party HTML-based crossword renderer and a mobile app, so today (in 2020) it's mostly useful for independent puzzles that are exclusively distributed in the Across Lite (puz) format.
This code has been sitting on a hard drive in the attic for several years. I suspect it could be updated with minimal effort for modern uses. The most obvious use case would be for embedding on independent puzzle sites.
The code was written in JavaScript using Google's Closure Library, and is fully optimized for the Google Closure Compiler. When compiled and served using gzip compression, the compiled code is less than 40 kilobytes over the network. A build file and sample scripts are included for compiling using Plovr. It's been about nine years since I last built the code, so I'd expect some effort (or luck) would be required getting a fresh build.