The Army has Rangers (big R). The Army, the Navy, and the USMC have rangers (small r). The Navy calls their rangers SEALs; the USMC calls their rangers Recon.
The concept of "rangers" (small r) goes back to units formed in the French and Indian Wars, such as Rogers Rangers, who travel light, living off the land or what they could carry on their backs or take from their enemies. After WW2, the Army formalized the process with specific units designated as "Ranger" and established a Ranger School and a uniform decoration (Ranger Tab) which successful graduates are permitted to wear even if they are not assigned to a Ranger-designated unit or command.
The Air Force has PJs, which are like rangers, but in a limited sense, since their focus is on the rescue of downed aircrewmen.