A wealth of electronic Kanban tools are emerging. Some have been around for a while and others are relatively new. Most charge a monthly or yearly fee. Some have a free option with restrictions. A few are completely free.
Many teams prefer using a physical Kanban board drawn on a wall or whiteboard. They like the experience of physical interaction and the visibility afforded by posting status on a wall for all to see.
Electronic Kanban boards are particularly useful for distributed teams or even for teams that allow members to work from home. If you have an interest in going wall-less, take a look at these options. (A few are currently in beta status.)
Those marked with an asterisk (*) are totally free as of the date of this posting. If you know of any Kanban software, please leave a comment with a link.