For complex projects with many tasks would be nice to set tasks not only in different columns but also different rows.
An interesting use case can be to divide tasks into sprints (milestones) keeping also them grouped into streams, as in the following mockup:
. +--------------+-------------+--------------+-------------+
. | Future | Release 1 | Beta | Alpha |
. | No Milestone | Milestone 3 | Milestone 2 | Milestone 1 |
+-----------+--------------+-------------+--------------+-------------+
| Stream 1 | ... | ... | ... | ... |
| | | | | |
+-----------+--------------+-------------+--------------+-------------+
| Stream 2 | ... | ... | ... | ... |
| | | | | |
+-----------+--------------+-------------+--------------+-------------+
| ... | ... | ... | ... | ... |
| | | | | |
+-----------+--------------+-------------+--------------+-------------+