Mine's reading temperature, humidity and pressure from sensors and uploading it to a VPS. My second one that is, my first one hasn't done more than collect dust.
If you mean a Raspberry Pi 1, try RISC OS.
Very un-Unix-like, predates Linux by nearly a decade. Single-core and goes very fast on a Pi 1.
Connectivity can tilt towards RPi, you can do vpn, ipv6, mobile data (if you use a usb stick), ethernet etc.
Funny thing is that modern 3G/4G/5G modems are full System-On-Chip computers themselves supporting virtualization. The Qualcomm Snapdragon MSM8916 is a popular SoC used for LTE dongles that runs the modem Baseband Real-time OS and Debian/Android OS on the same CPU.