Robust Formula Field
It would be great to be able to create custom formula fields (properties) in Hubspot like you can in Salesforce. I know of the existing calculated property option, but it's quite limited (only used on number fields).
The new formula field would allow a user to create a custom field based on expressions like Date/Time (e.g. WEEKDAYDIFF(date1, date2)), Average (e.g. AVERAGE(number1, number2[, ...])), Text (e.g. CONCAT(string1, string2[, ...])), and other (e.g. IF(condition, trueExpression, falseExpression)).