Group/Collection:
* Group
* Bunch
* Set
* Assembly
* Aggregation
* Congregation
* Gathering
* Pack
* Heap
* Pile
Closely packed group:
* Swarm
* Throng
* Mass
* Confluence
* Constellation
* Nest
Technical:
* Array
* Network
* System
Figurative:
* Constellation (referring to a group of stars)
* Galaxy (referring to a group of stars)
* Web (referring to a complex interconnected group)
For example:
* "A cluster of grapes" could be replaced by "a bunch of grapes."
* "A cluster of stars" could be replaced by a "constellation of stars."
* "A cluster of computers" could be replaced by a "network of computers."
The best synonym will depend on the specific context and the intended meaning.