Here's how developers Betacom SA describe the game on the App Store:
A crisis is brewing in Fruitopolis! The new year's produce of fruits and vegetables is ready, but it now needs to be distributed to local grocery stores as quickly as possible! Thousands of fresh and juicy apples, pears, and grapes could spoil if they aren't transported in time! Trains will be passing through every town, headed for Fruitopolis Central. Fill them to the brim with fruits and vegetables for your friendly neighbourhood grocer! Good luck, you'll need it!
Putting the plot aside, Loco is actually a Zuma styled arcade action game, where you'll be throwing the fruits towards the coloured targets on the trains as they pass. Unlike Zuma (and Zuma's Revenge, which is now available across the Windows Phone 8 range), a coloured fruit will only take out one coloured target on the train, while chain reactions are limited to just two targets next to each other.
The huge chains you could vanish in Zuma are not going to happen here, which changes the style of game you can play. Also tweaking the game is the ability to grab bonuses from the train with a claw on a chain coming from the central 'fruit thrower' you have.
Loco Train looks like it's going to be a clone, but in fact the changes made are subtle but strong enough to create a new game that has its own quirks and challenges. Loco Train is a free download from the AAWP App Directory, with a £1.99 in app purchase to unlock all the levels.