I'm mainly talking of the tools estate agents use to build their websites as well as manage their properties, clients etc.

You are right that getting listings is the primary pain point but I would have thought standards about how properties are categorised etc would help with this. In particular as real estate becomes more international it would really help for a broker in Mexico to be able to send details of a property to someone in Russia in a format that can be mutually understood.

I can also imagine a demand for open source tools that can help in the communication between all the different parties to the transaction. I have ideas about how such a tool could monetise and I'm surprised that no one else has thought to do it.