OpenKneeboard can be controlled from:
For other language, using the C API is strongly recommended; see the documentation for your language/framework for how to call C libraries.
If you are not comfortable calling C functions, the remote control executables provide a more limited API. You can locate them with:
..\utilities\
from theInstallationBinPath
registry value on v1.8.4 and above%PROGRAMFILES%\OpenKneeboard\utilities
on earlier versions (deprecated)