The 'KOSync' plugin will synchronize furthest reading progress
across different koreader devices after users registering their
devices.
The synchronizing service is open-sourced as the project
[koreader/koreader-sync-server](https://github.com/koreader/koreader-sync-server).
it uses non-blocking turbo I/O looper to process http request
so that multiple http request can be handled simultaneously and http request
won't block user input, and most importantly, in Lua's way.