Since Ledger's accounts and commodity system is so flexible, you can have accounts that don't really exist, and use commodities that no one else recognizes. For example, let's say you are buying and selling various items in EverQuest, and want to keep track of them using a ledger. Just add items of whatever quantity you wish into your EverQuest account:
9/29 Get some stuff at the Inn Places:Black's Tavern -3 Apples Places:Black's Tavern -5 Steaks EverQuest:Inventory
Now your EverQuest:Inventory has 3 apples and 5 steaks in it. The amounts are negative, because you are taking from Black's Tavern in order to add to your Inventory account. Note that you don't have to use ‘Places:Black's Tavern’ as the source account. You could use ‘EverQuest:System’ to represent the fact that you acquired them online. The only purpose for choosing one kind of source account over another is for generate more informative reports later on. The more you know, the better analysis you can perform.
If you later sell some of these items to another player, the entry would look like:
10/2 Sturm Brightblade EverQuest:Inventory -2 Steaks EverQuest:Inventory 15 Gold
Now you've turned 2 steaks into 15 gold, courtesy of your customer, Sturm Brightblade.