FLTK(Fast Light Tool Kit 发音为fulltick) 是一种使用C++开发的GUI工具包，它可以应用于Unix,Linux,MS-Windows95/98/NT/2000和MacOS操作系统平台，相 对于其它的许多图形接口开发工具包（如MFC、GTK、QT等），它具有体积很小、速度比较快，且有着更好的移植性。
FLTK 从 1.3 版本开始添加了UTF-8编码支持，为多国语言支持提供了基础。
Even though FLTK 1.3.5 does not fix all STRs we decided to release FLTK 1.3.5 as it contains many new features, bug fixes, and adaptations to new compiler releases.
One very important enhancement is support of macOS 10.13 "High Sierra" and 10.14 "Mojave". Apple changed internal draw functions in a way that older FLTK versions wouldn't work anymore out of the box with the latest macOS and developer files (SDK).
This release does not contain new "ABI features". The ABI (Application Binary Interface) is 100% compatible with releases 1.3.4, 1.3.4-1, and 1.3.4-2.