This is something I've been tinkering with for a while, but I think it's now complete enough to be generally useful. It's an alternative frontend for LessWrong 2.0, using the GraphQL API.
Features:
- Fast, even on low-end computers and phones
- Quickly jump to new comments in a thread with the "." and "," keys
- Archive view makes it easy to browse the best posts of years past
- Always shows every comment in a thread, no need to "load more"
- Log in and post using your existing username and password, or create a new account
- Simple markdown editor
- Typography enhancements
- Switch between fixed-width and fluid layouts and several different themes
- Easily view a comment's ancestors without scrolling by hovering over the left edge of a comment tree
Thanks to Said Achmiz for designing the themes and writing much of the frontend JavaScript.
Give it a try: https://www.greaterwrong.com
Yes, there's a more-or-less stable API, but it's not exactly documented. You currently have to figure it out by reading the LW 2.0 or GW source code and using Chrome dev tools to observe how it works. But it would certainly be possible to use it to create a native client.