Stand alone is an idiom meaning one who is unequaled or without peer, notice that the verb form is two separate words.
Standalone means an device or object that may operate independently from another system or object. Standalone may also function as an adjective, describing an independent object or device. Stand-alone is an acceptable variant.
The first known use of stand-alone, which has been for the most part shortened to standalone, occurred in 1966. Standalone is used mostly in technical and business jargon.
Hawks stand alone atop NHL: ‘You give them an inch, they took a mile’ (The Chicago Sun Times)
Wimbledon 2015: Novak Djokovic ends era of Big Four to stand alone (The Guardian)
And The Post does not stand alone, so the meaning of profitability is somewhat different from most newspapers. (The New York Times)
He stands alone as the active leader for most home runs by a visitor at the ballpark with 27 after providing a carbon copy of Friday’s first-inning solo home run. (The Global Post)
‘Star Wars’ standalone film will be Han Solo prequel, directed by Christopher Miller and Phil Lord (The New York Daily News)
Crude from Iran costs about $5 a barrel less than other varieties and standalone refineries such as MRPL are thus expected to gain from direct import from Iran. (The Economic Times)
Showtime’s upcoming stand-alone Net video subscription service has gained another home on Hulu. (USA Today)
House Republicans plan to breathe new life into President Barack Obama’s trade agenda on Thursday by bringing up a stand-alone bill to give the president expedited authority to speed major trade deals through Congress. (Huffington Post)