The open source service provider OpenHub displays an automatic estimate how much work must have gone into the projects they list. Of course this is a very rough estimate (based on the lines of code and the basic COCOMO model) but it now states the effort that went into Mustangproject may now exceed one million dollars and with their default values may have been as much as 18 man years and $1,004,027 (on Saturday, July 5th, 2025).
The potential error margin may be quite high, but on the other hand this estimate does not include work on the website, various speeches, or contributions e.g. in the Factur-X/ZUGFeRD standardization committee.
Anyway, thanks to all contributors! And thanks for contributing this (automatic) estimate!