The standard Arduino libraries (common for beginner Arduino projects) as well as wide list of contributed libraries can be found within the Arduino IDE itself.In Arduino IDE 1 (specifically v1.6.2 ...

The official Arduino blog explains a little more about the features, tweaks and enhancements you can expect to enjoy once you have downloaded and installed the latest Arduino IDE 1.6.9 : ...

The Arduino IDE is known for its user-friendly interface and wide adoption among those involved in electronics and programming, ... the Arduino IDE 2.3 also extends support to the Mbed core.