RIPE have been running Internet observatories for decades. I remember the members of the TTM (test-traffic measurement) project in the late 90s trying to get ISPs to install GPS receivers on the DC roof for accurate one-way latency observations.
The actual probes are tiny consumer grade routers (https://www.google.com/search?q=ripe+atlas+probe&tbm=isch) with a new firmware. RIPE provides these free of charge to volunteers (people and companies) who then run them in their network (e.g. homes and datacenters). (Of course larger form factors are available to volunteers with more in-demand locations.)
In return, volunteers get rewarded for uptime of their probes with credits that can be used to request custom measurements from the Atlas network.
There are probes _everywhere_; not just in terms of geography (https://atlas.ripe.net/results/maps/) but also in network locations that you cannot get access to via any other means; there really is no other service that comes close in terms of reach for global internet status testing.