Someday columns
Someday columns hold tasks that don’t belong to a day yet. Have as many as you like, three or six in a row.
Three or six in a row
Go to Settings → your calendar and set Someday columns to 3 or 6. With 6, Tweek adds empty columns if you have fewer. Switching back to 3 keeps all your columns, they just wrap into rows of three.
Add a column
Hover over a column, click the three dots in its top right corner and choose Add column. The new column appears right after it. Click its name to rename it.

Change the order
In the same menu, Move forward and Move backward shift a column one place right or left.
Hide a column
Fold a column’s tasks away: choose Hide in the same menu, and Show to unfold it. On iPhone and Android, tap the arrow next to the column’s name. The column keeps its name and place, and nothing is deleted.

An empty column has nothing to fold, so Hide and the arrow show up once it has tasks. A column hidden on the web stays open in the apps, and the other way round. In a shared calendar, the column folds for everyone in it.
Delete a column
Choose Delete in the same menu. The tasks in the column are deleted with it, so move the ones you need first. You always keep at least three columns, so Delete works once you have four or more.
On mobile
Adding, moving and deleting columns, and the 3 or 6 setting, are on the web. The apps show your columns and let you rename and hide them.