A truly free, automated "estim audio generator" does not exist in a safe, reliable form. Using Audacity manually or downloading community-tested free files is the only safe free path.
There are fantastic free tools available, each offering different approaches to creating estim audio. You can design complex, dynamic signals from scratch or use a full-fledged audio editor as your creative studio. Here are some of the best free options to get you started. estim audio generator free