RKill

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

Blocks unauthorized webcam access.

Anti low-level keylogger: Provides full system-wide key press protection, and target window screenshot protection.

Rootkit detection and removal utility.

A utility that disables a number of risky Windows features. These "features" are exposed by the OS and primary consumer applications, and very commonly abused by attackers, to execute malicious code on a victim's computer. So this tool just reduces the attack surface by disabling the low-hanging fruit.

A utility for configuring encryption protocols, cyphers, hashing methods, and key exchanges for Windows components. Useful for sysadmins on Windows Server.

Provides protection against software keyloggers. Encrypts keypresses at driver level, and decrypts at application level, to protect against common keyloggers.

Internet traffic control and monitoring tool.

Portable virtual keyboard. Useful for protecting from keyloggers when using a public computer, as it can run of a USB with no administrative permissions.

Blocks malicious background applications from taking screenshots.

A portable app that lets you disable core Windows features (such as Cortana, Edge) and control which data is passed to Microsoft. (Note: Free, but not open source).

A CLI utility that shows file version number, timestamp information, and digital signature details.

Detects infected USB removable devices.

Capture and interprets network traffic based on a set of rules, and depending on the interactions certain assignments are blocked. Open source, written in Go and delivered as a single executable.

Portable app with a GUI, that makes it really easy to safely block key telemetry features, from sending data to Microsoft and other third parties (It uses the Windows API to interact with key features of Local Group Police, Services, Tasks Scheduler, etc).