Creating Excel UDF’s with VBA

The other day I got a message from Chip Pearson, asking me about the Excel Formula Pack. So far I have 6 people who applied to join the private beta.

Chip was wondering if I would be using VBA, .NET, Add-in Express, Excel-DNA, or something else. I didn’t respond with a technical answer, because I thought it deserved a public discussion.

I mentioned that the criteria for Excel Formula ToolPak formula functions are:

a) They need to be extremely fast
b) They need to run natively on Windows and Mac
c) They need to run across a broad range of Excel versions

What would be the most appropriate stack to satisfy the criteria above?

Let me know your thoughts in the comments below.