AdaTutor is an Ada 95 tutorial program written by John J. Herro. It has been placed into public domain by John. It is a great tutorial although it only touches on Ada 95 and does not contain information for Ada 2005 and 2012.
Here I have the AdaTutor presented on this blog. You will still need to download the AdaTutor to fully making use of this tutorial, as some contents and assignment information are not in the tutorila directly.
If you want to run the tutor under Linux, this article AdaTutor – Running it in Slackware will give you an idea. Although it is mentioned for running it under Slackware, the procedure does not involve any distribution specific feature, it could apply to common Linux distributions with GNAT compiler.