iOS4 brought with it the ability to put apps and bookmarks into folders. Unfortunately, the implementation is quite limited.
iOS4 folders
Posted inHOWTO
FoldersInFolders: Tweak To Enable Folders Inside Folders On iOS4 Hits Cydia Store
This add-on allows you to take better control of your SpringBoard’s folders, by placing folders inside folders.
Posted inHOWTO
FoldersInFolders: Tweak To Enable Folders Inside Folders On iOS4 Available In Cydia Soon [video]
FoldersInFolders is a tweak developed by the same guy that made available SBRotator, and it enables folders inside folders on iOS4.