dcal - dynamic calendar
dcal is a minimalistic calendar for X.
In order to build dcal you need the Xlib header files.
Edit config.mk to match your local setup (dcal is installed into the /usr namespace by default).
Afterwards enter the following command to build and install dcal (if necessary as root):
make clean install
See the man page for details.
This is what mine looks like, but it's quite configurable