WPSiteSync is a product that aims to improve the process for deploying content on your website. It allows you to create or edit a post or page on a staging environment, and then deploy those changes to your live website.
It is similar to Ramp by Crowd Favorite, a plugin that at one time I enjoyed, however it hasn't been updated since 2014 and I doubt it's a huge priority for the company.
WPSiteSync is a collaborative project between the team at ServerPress (who makes the DesktopServer local environment tool) and Dave Jesch of SpectrOM Tech. The base plugin, which syncs posts and pages, is free on the WordPress plugin repository.
They intend to monetize via extensions for syncing users, custom post types, comments, and other features.
I like the idea of WPSiteSync and I'll try and test it out soon. At first I thought this was an attempt at more complete database merging, which the Delicious Brains team is trying to tackle with Data Hawk, but I'd think of this more as a content tool, not a full site tool. I look forward to seeing where they go with it; I think it's an area of WordPress that could do with improvement.