mTrip has just told us that the company will make 17 of its most popular iPhone travel guide apps free this Tuesday, Wednesday and Thursday. Five travel guides will be available for free today (normally US$5.99), and six others over the next two days. Here's what cities you can grab on what day:

Tuesday, December 18 (today)

• Paris
• Amsterdam
• Vienna
• Tokyo
• Budapest

Wednesday, December 19

• London
• Berlin
• Madrid
• San Francisco
• Dublin
• Shanghai

Thursday, December 20

• New York
• Barcelona
• Rome
• Istanbul
• Singapore
• Prague

All of mTrip's free (and paid) travel guide apps can be downloaded in the App Store here. Happy travels!