It's not quite vinegar and it's certainly not wine, but verjuice can be used as a substitute for either in cooking. Made from unripe grapes, verjuice has a delicately sweet flavor with a bit more green-grape tang than you get in a wine. Fusion's Napa Valley Verjus (the French spelling) is made by Jim Neal, a former Spago chef who went north to work with Hiro Sone when he opened Terra in St. Helena. Although verjuice can be used in sauce-making, braising and poaching, it is especially handy for dressing salads because it is more "wine-friendly" than vinegar--its tartness (largely from malic and citric acid) doesn't spoil the taste of wine the way vinegar's acetic acid does.
Available at Wally's in Westwood and Broadway Deli in Santa Monica.