Approach Guides Wine
iOS only; £1.99
Dozens of apps offer background details on regions, varieties, and food pairings, but some are more accurate and usable than others. Approach Guides Wine is the most complete and user-friendly. You can search by style, region, grape or food match, and entries are cross-referenced. It also supplies a guide to vintages for each region and plentiful maps (some more detailed than others).

Pocket Wine ((iOS only; £2.49 for full version) is another fun example. A bank of more than 100 varieties grouped by style, it has detailed information and extensive food-matching ideas.