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 ...

[Jean] has created an Arduino core that provides basic functionality on x86 hardware. Your code has full control over the computer, and there’s no operating system overhead to contend with.

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.