Importing / exporting e-mail contacts
Compatability through CSV files: When you export contacts to CSV (comma-separated values), the generated file is actually pretty similar to an Excel spreadsheet and can be viewed / edited by MS Excel or OOo Calc. If you make a couple of contacts in Outlook or Entourage, then export them to CSV, then open the file in Calc, you can take a look for yourself. Now older programs (for example, FileMaker Pro 6) might be able to export to CSV but might not have the column headers on the top row. Fortunately, you can just manually write them in by comparing the labels with the labels specified on the CSV you exported from the program you want to gain compatability with.
Case: professor has some ancient MS Word documents (from a legecy Office Mac version), can't open them anymore because Office doesn't have the filters needed to read the files.