How do I open .bin/.idx database files?

I'm attempting to open some database files used by a legacy application that I know almost nothing about. The databases appear to be in file pairs of a bin and idx, for example: Cust.bin and Cust.idx.

I have never seen this type of database before and wasn't able to find anything useful through Google. I also don't know what la开发者_JAVA百科nguage or tool the developer used for this app, but it seems that he used the default generic icon for his published executable. This is it:

Can anyone tell me anything about this application, what type of database it uses and how I might open the database myself?

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The program that was using this database was a custom written application by a former consultant.

I never did figure out what type of database he was using, or how to open it properly. But I did manage to extract all the data out of it. I opened the file up in EditPad and found that all records had fixed-length fields. With this knowledge I was able to easily write a small application to parse all the binary data and export everything to .csv

So I was ultimately able to get the data. Woot!