Or by signing up to an anonymous account on Reddit (there are several good subreddits for people who suffer from mental illnesses such as r/depression), or any

Or by signing up to an anonymous account on Reddit (there are several good subreddits for people who suffer from mental illnesses such as r/depression), or any of a huge number of traditional forum sites for that purpose. Or there's always 4chan. Even in the app space Secret hasn't cornered the market, there's Whisper for example which doesn't ask for your email address and doesn't show you your friends' posts. It's ridiculous to claim that Secret is the only option for that person.