LibreOffice » toolkit
"Abstract" windowing thing, UNO implementations of windowing stuff so that it can be used from Basic or Java. But also stuff that has no connection to Basic or Java.
Note that the "awt" here has no relation to the Java awt, as far as I know. It might be inspired by it API-wise, perhaps. (If you know differently, feel free to improve this README file.)
Note that toolkit/ is itself not really a toolkit, it is at root a reasonably simple wrapper of vcl/ - if you came here looking for a toolkit, please checkout vcl/ instead.