Ask HN: How do you sell the software of a failed business?

Hello,

My parents attempted running a holiday-booking venture that didn't go anywhere. In the process, they had a fairly advanced web app built with things like custom refund policies and self-service registration for the hotels.

This web app cost a lot and it would be nice to get back some of that money, so how would you go about recovering the cost?

Any failed business sale forums I don't know about?