AWOS is an Automated Weather Observation Service and it does just what the name says, Its similar to NOAA weather radio only it continuously broadcasts the weather at that one site only.
Unicom is usually used at airports to request fuel service or towing. During air shows they are sometimes used as an air boss freq. If the airport doesn't have a tower (Uncontrolled Airport) the airfield is often assigned a Unicom freq as a Common Traffic Advisory Freq (CTAF).
Here in Newhall, California just north of the San Fernando Valley the Unicom freq 123.025 is used by aircraft while transiting through the Newhall Pass to advise other aircraft of their location. There are three airports just south of the Newhall Pass, Van Nuys, Whiteman and Burbank Airport and all three airports have approach and departure paths that travel through the Newhall Pass so its not only busy but very dangerous. Around Los Angeles the Unicom freq 123.050 is used by helicopters and heliports.