You can use any Window Manager (WM for short) that has been built for TC. However only some of them support the menu system that TinyCore uses.

From http://forum.tinycorelinux.net/index.php?topic=3283.msg18979#msg18979

  * hackedbox
  * blackbox
  * fluxbox
  * openbox
  * icewm
  * jwm
  * jwm-snapshot (451)

all support Tiny Core dynamic application menu.

TC 1.x used jwm by default, http://joewing.net/programs/jwm/
TC 2.x uses flwm by default, http://flwm.sourceforge.net/