$LicenseServer (Built-in Mathematica Symbol)

$LicenseServer is a string that gives the name of the license server that is currently authorizing Mathematica to be run.

$Line (Built-in Mathematica Symbol)

$Line is a global variable that specifies the number of the current input line.

$Linked (Built-in Mathematica Symbol)

$Linked is True if the Mathematica kernel is being run through MathLink.

$MachineAddresses (Built-in Mathematica Symbol)

$MachineAddresses gives a list of strings specifying the current IP addresses associated with the computer on which Mathematica is being run.

$MachineDomains (Built-in Mathematica Symbol)

$MachineDomains is a list of strings giving the names of the current network domains associated with the computer on which Mathematica is being run.

$MachineID (Built-in Mathematica Symbol)

$MachineID is a string that gives, if possible, a unique identification code for the computer on which Mathematica is being run.

$MachineName (Built-in Mathematica Symbol)

$MachineName is a string that gives the assigned name of the computer on which Mathematica is being run, if such a name is defined.

$MachineType (Built-in Mathematica Symbol)

$MachineType is a string giving the general type of computer on which Mathematica is being run.

$NewMessage (Built-in Mathematica Symbol)

$NewMessage is a global variable which, if set, is applied to the symbol name and tag of messages that are requested but have not yet been defined.

$Notebooks (Built-in Mathematica Symbol)

$Notebooks is True if Mathematica is being used with a notebook-based front end.