This build of Steam Desktop Authenticator works, but we cannot guarantee its stability. In addition, it lacks major polish that any reasonable application would have.
Please note that using the Steam Desktop Authenticator instead of the Steam Mobile Authenticator is a security risk. Data (not your password) is stored, unencrypted, on your hard drive. If someone were to gain access to your computer and steal these files, they could easily steal your items or account. This program is not endorsed or supported by Valve Software, and use of this program should only be considered if you cannot use the Steam Mobile Authenticator.
Download the binary and extract it to its own folder, preferably somewhere that it can stay forever. Adding an account is a straightforward process. After you add an account, a file containing all the data needed for the application is stored in a .maFile (JSON) in the "maFiles" directory wherever the program is executing from. It's highly recommended you back up this data (securely).
Confirmations (of trades and account setting changes) work, but only show you the names of the confirmations -- you can't see the actual details of a trade you're confirming yet.
You can add theoretically infinite accounts to this.