To arrange windows, drag one window by pressing center button and drop onto another window's tab. Right click displays a menu and from there you can freely change Tab's display location.
fluxbox can use Dock in Window Maker and Afterstep. Its display location can be specified any location on the outer circumference of a window. Also right click on slit gives a menu for changing location. The setup configuration will be saved as ~/.fluxbox/init when fluxbox is terminated. In order to use, invoke Dock in Withdrawn mode by adding parameter option -w or -d.
asclock -d & wmcdplay -w &
Blackbox's bbtools can also be used. However, bbkeys can not be used since fluxbox itself has an equal function to it. Also there is a wall-paper change assistant tool, bbrb. fluxbox-0.1.6 can start bbrb but it can not change wall-paper. After 0.1.7 it seems it would be likely to work.
Also, similar to Dock, to place it in slit, start it with -w option.
gkrellm, in a similar manner, can be put in slit by starting it with -w option so that you don't need to start it on every workspace and gkrellm comes on every workspace.