This framework has the potential to become another Qt if UI is been added. The coding style and document[0] are solid and similar with Qt[1]. Giving the Qt is heading in an unpopular way[2], I am looking forward to this framework.
Neat! I checked the async.h, looks like it doesn't support nested calls?
I did a similar toy many years ago, which could be used with other async libraries such as libuv: https://github.com/huxingyi/c-block
[0] https://plywood.arc80.com/docs/modules/runtime/api/string/St... [1] https://doc.qt.io/qt-5/qstring.html [2] https://www.qt.io/blog/qt-offering-changes-2020