synergy
mouse & keyboard sharing via LAN.
Lan Mouse is a cross-platform mouse and keyboard sharing software similar to universal-control on Apple devices. It allows for using multiple PCs via a single set of mouse and keyboard. This is also known as a Software KVM switch.
Share a single keyboard and mouse between multiple computers.
Deskflow is a free and open source keyboard and mouse sharing app. Use the keyboard, mouse, or trackpad of one computer to control nearby computers, and work seamlessly between them. It's like a software KVM (but without the video). TLS encryption is enabled by default. Wayland is supported. Clipboard sharing is supported.
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Barrier is software that mimics the functionality of a KVM switch, which historically would allow you to use a single keyboard and mouse to control multiple computers by physically turning a dial on the box to switch the machine you're controlling at any given moment. Barrier does this in software, allowing you to tell it which machine to control by moving your mouse to the edge of the screen, or by using a keypress to switch focus to a different system.