Fail2ban is a quick to deploy, easy to set up, and free to use intrusion prevention service that protects your systems from brute force and dictionary attacks.
If you are looking for an audio editing and creation tool, Audacity lets you create and edit professional audio files at no cost, all while using your existing hardware.
What cannot be measured cannot be improved. Netdata lets you measure almost anything – at least as long as it's about the performance and health of a Linux computer.