General:
* United
* Combined
* Joined
* Allied
* In unison
* As one
For physical proximity:
* Side by side
* Close
* Near
* Alongside
* In company
For cooperation:
* Collaboratively
* Jointly
* In tandem
* In partnership
* As a team
For agreement:
* In accord
* In harmony
* In unity
* Consistently
* Unanimously
More informal:
* As a group
* As a bunch
* Hand in hand
* In sync
* Togetherness
Specific examples:
* Instead of: "They worked together on the project."
* You could say: "They collaborated on the project."
* Instead of: "The children played together in the park."
* You could say: "The children played side by side in the park."
Choose the replacement word that best fits the specific situation and desired meaning.