What are the boolean literals in PowerShell?
$true and $false.
Those are constants, though. There are no language-level literals for booleans.
Depending on where you need them, you can also use anything that coerces to a boolean value, if the type has to be boolean, e.g. in method calls that require boolean (and have no conflicting overload), or conditional statements. Most non-null objects are true, for example. null, empty strings, empty arrays and the number 0 are false.