wmsupermon is a universal monitoring dockapp. It can be used to monitor CPU usage, disk I/O, memory usage, swap, filesystems, space utilization, network traffic, wireless link quality, CPU frequency, CPU temperature, fan speed, voltages (without requiring lm_sensors), battery status (with actual, not "reported", discharge rate), traffic from your router, or anything else. It can open and maintain many dockapp windows with one dockapp process.
libDockApp is a simple library for easily writing Window Maker dock applications, also known as dockapps (those that only show up in the dock). It is very limited and can only be used for dockapps that open a single appicon for each process in only a single display, but this seems to be enough for most, if not all, dockapps.
wmbday is a small dockapp that reminds you of birthdays. It can take an arbitrary number of birthdays, and will display the next four upcoming birthdays. By left-clicking a name, you can see the remaining days until the birthday. The colours of the background and the font can be customised.