Open calls for tender are very well defined with detailed specifications and tight rules and criteria. They open to everybody, including for-profit organisation, so ET would be in competition with established think-tanks, universities and consultants with a robust background in the field.
"open calls for proposals" are, well, open, which means they don't have detailed specifications. However, they must fit in the policy framework and still follow the same tight rules. They are only open to public organisations, universities and non-profit organisations. "Dieu se rit des hommes qui se plaignent des conséquences alors qu'ils en chérissent les causes" Jacques-Bénigne Bossuet
