Here's what the developers say:
"While we work with labels and publishers on a paid
Riffstation service, Riffstation will no longer be
available on the web or mobile devices.
hope to bring a similar service back in the future,
but in the meantime, we'd like to offer you a free
copy of Riffstation Pro desktop app (normally
$34.99), on us.
Riffstation Pro is an amazing tool for beginners and
advanced guitar players and will help unlock your
potential as a guitarist.
you in advance for your patience as we work on
NOTE: This is a desktop app for Mac and PC
computers and will not run on iOS and Android
devices. It works with audio files stored on your
computer as opposed to YouTube videos.