Gridsync aims to provide a cross-platform, graphical user interface for Tahoe-LAFS, the Least Authority File Store. It is intended to simplify the Tahoe-LAFS installation and configuration process and ultimately provide user-friendly mechanisms for common use-cases like backing up local files, synchronizing directories between devices, and sharing files and folders with other users across all major desktop platforms (GNU/Linux, macOS, and Windows). More broadly, Gridsync aims to duplicate most of the core functionality provided by other, proprietary "cloud" backup and synchronization services and utilities (such as Dropbox and BitTorrent Sync) but without demanding any sacrifice of the user's privacy or freedom -- and without requiring usage or knowledge of the command line. Accordingly, Gridsync is developed under the principle that secure file storage should be freely available to everyone, without exception, without added barriers, and regardless of one's operating system choice.
Tahoe-LAFS already provides a number of highly desirable properties for secure file-storage: in addition to offering client-side encryption, it is decentralized, robust, free (as in both beer and speech), stable and mature, and written by a group of very talented developers. Unfortunately -- and despite all of its technical merits -- Tahoe-LAFS has a number of persistent usability issues which steepen its learning curve: its installation requires manual compilation from source on Windows and macOS, its configuration consists in hand-editing text files, its primary interface requires heavy command line usage, and many of its fundamental concepts (e.g., "dircap", "shares", "servers-of-happiness") are opaque to new users or otherwise demand additional reading of the project's extensive documentation. Accordingly, Tahoe-LAFS' userbase consists primarily in seasoned developers and system administrators; non-technical users are naturally excluded from enjoying Tahoe-LAFS's aforementioned advantages.
An invite code is a short combination of numbers and words (e.g., 9-hamburger-chairlift, 1-forever-alone) that allows two computers to communicate safely with one another. By knowing and using the same shared "invite code," any two parties can quickly and easily establish a secure connection through which additional sensitive information (like passwords or other credentials) can be transmitted. Learn more about invite codes
A digital signature is a small segment of text that, like a traditional "physical" signature with a pen on paper, represents the certification of a given document or file. In the same way that a person might sign their name at the end of a letter, software developers will sometimes "sign" their applications and make those digital signatures available for download – typically in the form of small ".asc" or ".sig" files offered alongside the main application. Generally speaking, whenever a developer provides links to digital signature files, it is a good idea to download them with the application and to verify them before running the associated application.
Unlike signatures made with a pen on paper, digital signatures, when correctly implemented, are extremely difficult to forge. Because proper digital signatures rely on public-key cryptography, only persons who posses the "signing key" that corresponds to a particular identity can generate digital signatures on behalf of that identity. Mallory, for instance, cannot sign files using Bob's identity unless she also possesses Bob's privately-held signing key; so long as Bob is the only person in possession of his signing key, it is reasonable to assume that any files digitally signed by Bob's key came from Bob himself.
For more information on Gridsync, you can check out the github repo for the project.