ClamTk

Clears cache and deletes temporary files very effectively. This frees up disk space, improves performance, but most importantly helps to protect privacy.

Locally checks for signs of a rootkit.

Firejail is a SUID sandbox program that reduces the risk of security breaches by restricting the running environment of untrusted applications using Linux namespaces and seccomp-bpf. Written in C, virtually no dependencies, runs on any modern Linux system, with no daemon running in the background, no complicated configuration, and it's super lightweight and super secure, since all actions are implemented by the kernel. It includes security profiles for over 800 common Linux applications. FireJail is recommended for running any app that may potential pose some kind of risk, such as torrenting through Transmission, browsing the web, opening downloaded attachments.

Open source GUI firewall for Linux, allowing you to block internet access for certain applications. Supports both simple and advanced mode, GUI and CLI options, very easy to use, lightweight/ low-overhead, under active maintenance and backed by a strong community. Installable through most package managers, or compile from source.

Open source intrusion prevention system capable of real-time traffic analysis and packet logging.