Radio Silence
Radio Silence is a network monitor and firewall for the macOS. The software stops apps from making network connections. The firewall runs in the background and does not require an open window.
20 Alternatives To Radio Silence

Atento for Mac
Avoid procrastination and distractions at work
Comodo Firewall
Comodo Firewall Pro - Secure your system against internal attacks such as Trojan viruses /…
Firestarter
Firestarter is an Open Source visual firewall program.
Focus
New Tab page that gives you a moment of calm and inspires you to be more productive.

GlassWire
Visualize network activity in detail, get notified when new apps access the network, look out for…
Hyperfocus
The distraction blocker for macOS

Little Snitch
Little Snitch is a firewall application that monitors and controls outbound internet traffic.

Mobiwol
Mobiwol is a NoRoot Firewall
NetGuard
NetGuard
OpenSnitch
OpenSnitch is a GNU/Linux port of the Little Snitch application firewall.
RescueTime
Time management software that shows you how you spend your time & provides tools to help you be more productive.
Shepherd
Opens quality content you choose instead of Facebook/Twitter
Smiling Mind
Promotes mindfulness and meditation for young people
Space
Get a fast, unlimited desktop in VR
Teeny Breaks
Mindfulness tips to make the most of your breaks í ¾í· í ½í²
TinyWall
Lightweight and non-intrusive firewall
TripMode
Manage your Mac’s broadband usage while on a hotspot

Windows 10 Firewall Control
Windows 10 Firewall Control: simple and exhaustive solution for applications network activity controlling and monitoring.
ZoneAlarm Free Firewall
Personal Firewall software
simplewall
Simple tool to configure Windows Filtering Platform (WFP) which can configure network activity on…