Portmaster

GlassWire

GlassWire is a network monitoring and personal firewall application for Windows and Android that visualizes current and past network activity to help users spot malware, bandwidth hogs, and unfamiliar devices on their network. Its firewall includes an ask-to-connect mode that lets users approve or deny individual apps' network access, alongside a network time machine for reviewing historical connections. GlassWire also tracks data usage across devices and can alert users before they exceed set data limits, while its network scanner flags new or unknown devices joining a WiFi network. Over 53 million downloads have been recorded for the Windows and Android apps combined.

OpenSnitch

OpenSnitch is a GNU/Linux interactive application firewall inspired by Little Snitch. It allows users to intercept and control outgoing network connections, providing a high level of security and control over the system's network activity.

LuLu

LuLu is a free and open-source firewall for macOS built by Objective-See, designed to monitor and control outgoing network connections rather than inbound traffic. It alerts users whenever an unknown or unrecognized process attempts to connect out to the network, helping catch malware trying to exfiltrate data or reach command-and-control servers.

Little Snitch

Little Snitch is a network monitoring and application firewall for macOS made by Objective Development. It intercepts unwanted outgoing connections attempted by apps, installers, and background processes, and lets you decide - on a per-app, per-domain, or per-port basis - whether to allow or deny them. Beyond blocking, Little Snitch visualizes network traffic with interactive charts covering up to 12 months of history, organizes activity by app, domain, or country, and offers built-in DNS encryption (DoH/DoT/DoQ) plus daily-updated blocklists. Rules can be grouped, shared, and automatically switched based on the current Wi-Fi network.

NetLimiter

NetLimiter is a Windows utility for controlling and monitoring network traffic on a per-application basis, letting users set maximum upload/download speeds for individual apps, the whole system, specific users, or individual connections. It shows real-time traffic with live visualization and keeps long-term local statistics for historical analysis. Interactive rules can block selected applications from reaching the internet based on conditions like application path, domain, IP range or user account, and data quotas can automatically throttle or block traffic once a transfer limit is hit. It is sold under Locktime Software as a Pro edition with time-limited licenses covering one or two-year usage periods.