Ghostrak is the video tool baseball and softball training facilities use in the cage. A coach films a swing or a pitch, plays it back frame by frame, and lays it over an earlier rep so the difference is something you can actually see rather than describe.
Ghostrak is not a consumer app you sign up for. Access comes from the facility you train at: they create your account, and the app signs you in through that facility's own system. Download the app, choose your facility on first launch, and sign in with the account they gave you.
If your facility does not use Ghostrak yet, ask them — nothing on this page will get you an account.
Most people Ghostrak films are children. That shapes the whole product: clips are unlisted rather than public, rosters are visible only inside the facility, and nothing is sold, shared with advertisers or used to build a profile. The privacy policy says exactly what is recorded, who can see it, and how to have it removed.