Air traffic control employers
You apply to the organisation that provides air traffic services where you want to work. There is no shared worldwide employer.
That organisation may be a government agency, a state-owned provider, or a company. An announcement from one of them does not describe hiring at another.
NATS
NATS provides air traffic services in the United Kingdom and employs civil controllers for the units it staffs. It does not staff every airport tower. Recruitment campaigns are published by NATS.
FAA
In the United States, the Federal Aviation Administration employs civil air traffic controllers. Hiring announcements are published by the FAA.
NAV CANADA
NAV CANADA provides civil air traffic services in Canada and publishes its own controller recruitment information. See NAV CANADA.
EUROCONTROL
EUROCONTROL recruits controllers for the Maastricht Upper Area Control Centre. That recruitment is separate from the national providers in the countries around it. See EUROCONTROL and its student controller recruitment.
Other countries have their own providers. Country-by-country notes belong under Countries. The hiring document itself is covered under Recruitment.