Simple Unix Events (SUE) Library is a small and light-weight set of C++ classes which lets you easily create an event-driven application with C++ under Unix.
You might want to take a look at the Doxygen-generated documentation.
The library is available under the terms and conditions of GNU Lesser General Public License, v. 2.1.
The last version is 0.2.71 and it is available for downloading here via ftp and here via http.