The JUCE cross-platform C++ framework.
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README.txt

# The JUCE Library

JUCE (Jules' Utility Class Extensions) is an all-encompassing
C++ framework for developing cross-platform software.

It contains pretty much everything you're likely to need to create
most applications, and is particularly well-suited for building
highly-customised GUIs, and for handling graphics and sound.

Most JUCE modules are shared under the GNU Public Licence
(GPLv2, v3, and the AGPLv3). This means that the code can
be freely copied and distributed, and costs nothing to use
in other GPL applications. The juce_audio_basics,
juce_audio_devices, juce_blocks_basics, juce_core and
juce_events modules are permissively licensed under the ISC.

For more information, visit the website:
http://www.juce.com