General Synonyms:
* Cooperation
* Teamwork
* Partnership
* Joint effort
* Mutual effort
* Synergy
* Interdependence
* Concurrence
* Conjunction
* Alliance
More Specific Synonyms:
* Co-creation: Emphasizes a shared creative process.
* Co-design: Focuses on designing something together.
* Co-development: Indicates joint development of a product or idea.
* Joint venture: Implies a formal partnership.
* Synergistic effort: Emphasizes the combined effect being greater than the sum of its parts.
The best synonym for "collaboration" will depend on the specific situation and the desired nuance.