Learn English – A word to describe something that has a clear-cut purpose and consequently works out of the box

I'm looking for a word that would convey the idea of something that adresses a definite problem set and consequently lets you do so without much effort.

Here's an example:

• Hammers are designed to drive nails
• Hammers are consequently very easy to use to achieve that exact purpose
• (And not very good at doing something else)

A small twist: I'm looking for words that emphasize the "designed to" aspect.

For example, appropriate wouldn't be entirely – well – appropriate because it conveys the idea that the tool happens to fit the bill, not that it was designed with the purpose of doing so.