What kind of device would you like to be added :
PostNL Track & Trace.
Or rather: much more like, DHL, UPC, DPD, etc. Or combined services like 17Track.
What kind of category signal would the app use :
Internet
Is there a (public) API / documentation or known other implementations (like Blogs/Github etc)
https://www.ups.com/nl/en/services/technology-integration/online-tools-tracking.page?loc=en_NL
https://developer.dhl.com/api-reference/shipment-tracking#get-started-section/overview
http://diswiki.dpd.nl/
Are you willing to loan or donate a device or money to a developer?
Yes, definately!