Site or node on the Internet where similar propositions are coalesced. This will require human intervention, probably in the form of debate in the first instance between the parties who proposed the similar propositions.
At it's most primitive, email discussion between the parties will be necessary, but there remains the question of how similar propositions will be identified in the first place.
Keyword search engines may be used to play a part in detecting similar propositions.
Arbitration services may be required to assist in disputes over coalescence.