A rather hard to find ingredient that is used in some Caribbean cocktails, most notably in the Bermuda Rum Swizzle. It is essentially a sweet syrup that is flavored with lime juice, ginger, and other spices. While Grenadine is often used as a substitute, I feel that it really isn't quite the same.
For a long time, Falernum had been made by Sazerac Co., but due to apparent lack of sales, they stopped producing it several years ago. To help fill in the gap, Da Vinci Gourmet (a flavored syrup company) started producing a non-alcoholic version that could be used in cocktails that required Falernum.
"Fee Brothers" is also now producing a non-alcoholic Falernum syrup as well, flavor-wise it provides a very similar profile to the DaVinci Gourmet version.
Just recently, a brand of Falernum from Barbados is being distributed through "Spirit of Hartford", and comes highly recommended by Dale DeGroff. I unfortunately have not yet been able to obtain any of this.