Looking for a tool that gives a score based on the likely hood of a 0-confirm deposit being douple spent I know there is gap600, but it's proprietary, closed source and most likely expensive. If there is an open source free solution then please let me know.
Zero-confirmation transactions are inherently unsafe to be considered as completed payments. It is not possible to create a tool that could give a truly reliable indication of whether or not an unconfirmed transaction will in fact confirm (or not). If it were possible to reliably predict such a thing, we wouldn't need a blockchain record in the first place.