Tourism is a multi-billion dollar industry and it's hardly a surprise that many large and small software companies are offering various tools to help the traveller on the road. Tools are available for almost all kinds of operating systems.
While this site cannot suggest any particular application (for there are hundreds created each day), there are some guidelines applicable to any operating system, tablet or smartphone.
Generally, when travelling you usually need the following types of applications:
GPS,Map and other navigation software, such as Metro lines or Bus schedules.
Photo/Video software can help you enhance your photos or videos after taking them.Photo/Video editing software is almost exclusively available only in desktop/laptop computers due to the need of high processing power.
Using photo/video software requires the following:
A deep wallet. While there are many freeware options, the most serious tools are expensive.
A good computer. With nowadays cameras that shoot video in 1920x1200 resolution, processing that video with a slow computer could take you weeks before your videos are edited. That's also where multi-core processors show their power, for video/photo editing software span their processing throughout all CPU cores.
Knowledge and understanding of many scientific aspects. Photo software is not the kind of application which you merely navigate through the menus and find out your way. It requires scientific knowledge about quite a lot of detail in order to become useful. Otherwise your images may be rendered worse after processing.
Time. Editing and fixing shots is way slower than taking them.
Online maps are sometimes used with combination of offline maps in order to provide more accuracy and some extra features like street congestion information.
Instant Messaging software allows you to communicate with your friends and share messages/files with them.
VoIP software allows you to use the internet to make phone calls and/or send sms messages, when using the GSM network would be more expensive.
Photo/Video sharing software allows you to share your photos/videos directly from your smartphone.
All these tools are available for almost all mobile platforms (smartphones/tablets). A common mistake of many users is to use an application fine at home, only to find that it is not usable while travelling because it needs internet connection, some times a fast one. For example, the popular Google Earth needs an internet connection, so it would be useless if you try to use it without internet or quite expensive if you use it over 3G.
Either verify that your software works "offline" or get an offline version of it.
Windows, OSX, Linux or other Desktop Computers
While mapping software exists for desktop computers, it's unlikely that you will ever need it, for desktop computers are not portable and therefore most valuable software for travelers like GPS/map software would be quite useless when used in a computer that must remain on a desktop.
On the other hand, Photo/Video software almost exclusively runs in desktop/laptop computers only, due to the high processor power that is needed to process multimedia.