General Synonyms:
* Along with
* Together with
* Simultaneously
* Concurrently
* Alongside
* In combination with
* In collaboration with
* In association with
* Jointly
* Cooperatively
More Specific Synonyms:
* In tandem with (implies a close connection and working together)
* Hand in hand with (implies a close partnership)
* In harmony with (implies agreement and compatibility)
* In coordination with (implies a planned and organized effort)
* In sync with (implies a close alignment and timing)
The best synonym to use will depend on the specific situation and the meaning you want to convey.