Is there/ is it possible to send data to piwik from a c# application or something like that?
See libs/PiwikTracker for the PHP tracker (and soon, libs/PiwikTracker/java).
Any documentation or something on how to use it?
try c# socket for coonection How to C# Socket programming
C# API Clients are now available : C# Tracking and Analytics API Clients Available Now - Analytics Platform - Matomo