This MSDN article lists various functions that can be used in SharePoint calculated columns, and also includes the following disclaimer:
Microsoft SharePoint Foundation formulas for calculated fields are based on Microsoft Excel functions and syntax. However, Microsoft supports only those functions mentioned on this page for use in SharePoint Foundation calculated fields. For example, the Excel function MID is not supported.
That article is for SharePoint Foundation (the free version). Microsoft used to have a similar article for SharePoint Server, but I can't find it - maybe they deleted it. (SharePoint Server does support
MID, by the way.)
Regardless, there are certainly numerous other similar articles that list Excel functions you can use in SharePoint, but does there exist a list of those functions you cannot use?
(I realize that the number of supported functions is probably a small percentage of the complete list of Excel functions. So I'm not looking for a complete list of every unusable Excel function in SharePoint; just those that are likely to be needed in the same contexts as others that are supported. For example,
SUBSTITUTE (searches a string for all occurrences of one substring and replace them with another substring) is not supported, but
REPLACE (replaces whatever character is at a specific position in a string with another character) is.
In other words, what are the functions that you can't use in SharePoint, that a person used to writing Excel functions would most likely be surprised to learn do not work?