Example from angela_a:
We recieved a batch of digital images and are not able to define what imageformat they are saved in and what software to render them with. Could you help me with this task and explain how to proceede in such a situation? they have a suffix ".ch" and are fairly large (ca. 18 Mb) Someonw have an idea?
One good starting option is to use the FITS tool, which combines a number of tools in order to identify and describe files.
See The Registry for more lists of tools.
Oh, and having looked up the '.ch' extension, I think it's likely that the extension is simply wrong, but of course it could always be really some obscure format. Identification tools should be able to determine this quickly enough.