asmcmd - command line interface to ASM
When ASM was released the asmcmd was useless. Today, in version 11gR2, the asmcmd is a truly versatile and useful tool.
ASMCA - ASM configuration assistant
ASMCA has two flavours - the pretty one, with the graphical user interface and the silent workhorse. While the GUI version is certainly useful, it's the silent asmcmd that is the powerful one.
kfed - ASM metadata editor
I have talked about using kfed to perform a health check on your ASM metadata blocks, have a closer look at ASM disk header and how it can be useful in mapping ASM disks to OS device names.
While kfed is not just a reader - it is a true editor - I did not talk about editing ASM metadata blocks as any such activity would render your ASM and database unsupported. As with other Oracle block editing tools, their use is limited to Oracle Support for data salvage and data export purposes only.
amdu - ASM metadata dump utility
This is also an unpublished utility, so I have to careful with my posts about it. It is most useful to Oracle Support, but it is good to at least understand what it can do. As its name implies, it can read and dump ASM metadata, but unlike kfed, it can extract database datafiles. And like kfed, amdu does not need the ASM instance up or the disk group to be mounted!
kfod - ASM discovery tool
This is a specialised tool that does one thing only - it discovers ASM disks. It is used during the software installation, but it can be used on its own at any time. Indeed, when ASM has problems mounting the disk group and in particular when it complains that it cannot find a disk(s), quick kfod run may prove a valuable diagnostic aid.
renamedg - disk group rename
Another specialised utility - it can be used to rename any disk group.
Caution should be exercised with this utility as it is not integrated with the rest of the software stack. That means it does not talk to the Clusterware, ASM or the database. While ASM can simply discover a new disk group, by means of reading disk headers from the disks it finds in the discovery path, your database would not have a clue that its files are now in a renamed disk group.
cellcli - Exadata storage cell command line interface
Now this is not an ASM tool. But understanding cellcli is essential for those lucky enough to have Exadata.
Hey, don't forget the sqlplus! It is still the most powerful ASM management and administration tool.