With Rosetta Stone, you have the choice between around 30 different languages, from the more well-known ones such as French, German, Spanish and so on to some rather more obscure ones (conversational Pashto, anyone?), so it really depends on what you fancy.
There are 3 levels to each language (some even have 5), meaning you can really start from the basics and work upwards. In terms of where it’ll get you: Levels 1-3 will bring you up to CEFR Level A2 (a description of the different levels can be found here) and levels 4-5 will take you up to CEFR Level B1.
The Mac version of Rosetta Stone runs on Mac OS X 10.4 onwards (PowerPC and Intel processors) and to really enhance your language learning experience, a microphone or a headset with a built-in mic is ideal (I’ll explain why later). The application is relatively simple to install and once you’ve gone through installing it and the relevant language pack(s) you’ll be asked to give your name (multiple users are also possible) and what kind of course you want to do.
Rosetta Stone allows you to select different types of course depending on what skills you prioritize. If you are simply wanting to brush up on your skills before you go on holiday, for example, then you can select a shorter version of the course which focuses on, say, speaking (however seeing as the course costs about the same as an average return flight to Europe from the UK, I doubt you’ll be using it for just that).
For the best language learning experience (and to get the most out of the product), you’re best selecting the whole course which takes you through everything. Once you’ve selected your course you arrive at the home screen.