Data modules are small add-on libraries for remoteStorage.js, which extend it for storing certain types of data. App developers can create and use these modules to access and manage the same data in different apps.
Data modules are currently defined per category (the base directories, which an app requests/receives access permissions for). For example, there's a "bookmarks" module, which can be used to manage data in the "/bookmarks" directory of a user's storage account.
A module defines data types, which will be used to validate incoming data as well as adding JSON-LD contextual metadata. Type formats are being defined using JSON Schema, and incoming data is validated against the schemas defined in the module by remoteStorage.js.
(May 2017) We used to maintain data modules in a single shared repository on GitHub until recently. However, with the library layout and module loading changes in the upcoming remoteStorage.js 1.0, we decided to migrate all modules to their own user-managed repositories and use npm for module- and package management.
We're encouraging module authors to use the tag/category/keyword "remotestorage-module" on GitHub, npm, etc. so that app developers can easily find rs.js data modules in the future.