Facebook Pixel vs Piwik: What are the differences?
Developers describe Facebook Pixel as "A piece of code for your website that lets you measure, optimise and build audiences for your advertising campaigns". A code that you place on your website. It collects data that helps you track conversions from Facebook ads. On the other hand, Piwik is detailed as "The ultimate open source alternative to Google Analytics". Piwik is a full featured PHP MySQL software program that you download and install on your own webserver. Piwik aims to be a Free software alternative to Google Analytics, and is already used on more than 1,000,000 websites. Privacy is built-in!.
Facebook Pixel and Piwik belong to "General Analytics" category of the tech stack.
Piwik is an open source tool with 11.7K GitHub stars and 1.81K GitHub forks. Here's a link to Piwik's open source repository on GitHub.