I meditate with Prana breath off and on for about 5 years. I like that there is no taking and a variety of training options. There are audio and visuals as well. I've calmed myself from a panic attack using this app.
I also use downdog app to try to practice every day. Again there is a lot of customization on voice type, length, style and directions. This has been the best at home workout for me and I've tried a lot of different things from P90x, pelaton, to a rowing machine, etc.
Basically, I've tried almost anything an article and therapist has recommended to me over my mental health journey. The thing I've finally realized is to pick up each thing, when I need it. It may not be every day and definitely not the same thing in a week, but to try to do something daily. This seems to fit my personality the best.
I hope this helps someone on their journey!
Not free, but this book is a great Primer on Positive Psych and includes many exercises demonstrating the concepts in each chapter, perhaps your local library can get you a copy. Also a vaguely remember a Harvard or Stanford Positive Psych class on coursera which is interactive and free.
Honestly, it sound like he may need a help of a trained professional. If he is depressed, he should seek help. If he won't get counseling, I would try to find out why and be supportive through that process. Depression requires the help of a trained professional and there are a lot of resources and different approaches out there. Asking for help is not a sign of weakness, it's a sign of strength. If you had a physical malady, you would go to the doctor. Emotional maladies are the same. If you are interested in books to help with changing attitudes and thinking, I'd encourage you to read Learned Optimism by Martin Seligman and the Resilience Factor by Karen Reivich and Andrew Shatte