Free open source alternative app list of Comodo :

Let's Encrypt

A nonprofit Certificate Authority providing TLS certificates to 363 million websites.

FreeWindowsmacOSLinux

ZeroSSL

SSL ProtectionFor AnyoneFast. Reliable. Free. Easily secure any site by putting SSL management on autopilot, supporting one-step validation and renewal via REST API. Free SSL certificates issued instantly online, supporting ACME clients, SSL monitoring, quick validation and automated SSL renewal via ZeroSSL Bot or REST API.

FreemiumWindowsmacOSLinuxAndroidiOS

Others are looking for free open source alternatives of following apps:

Acorn 7

Acorn 7 is a Mac image editor for editing photos and creating graphics.

AI & Machine Learning

Free open-source AI & machine learning tools.

Ad Blocker

Ad Blocker is a browser tool that removes intrusive ads and pop-ups from web pages.

AdGuard

AdGuard is a cross-platform ad blocker that filters web content and protects privacy.

AdGuard DNS

AdGuard DNS is a DNS-based service that blocks ads, trackers, and malicious websites.

Adobe Premiere Pro

Adobe Premiere Pro is a professional video editing software for film, TV, and web.