Jammit Resurrected

Download the Modified Official Client v1.0.0.8 (Windows)
Download the Open-Source Client v0.3.0 (Windows/.NET)

Pick a client above, register an account here, and log in with the client.
Then reclaim your songs from the "store", and enable them for each device you sign in with.
Finally, just check for downloads in the client to begin downloading your songs.

You can use this server with the official Jammit client!
Simply replace all instances of "jammit.com" (both ASCII and Unicode) with "jammit.rip" in the .exe.
(Or just download the modified client from the link above)

The open-source "Jam.NET" client can also use this server.
You can download it at AppVeyor and use jammit.rip as the server.
(Or just download the pre-configured client from the link above)