Formal:
* Completed
* Concluded
* Finished
* Terminated
* Accomplished
* Achieved
Informal:
* Done
* Over
* Wrapped up
* Through
* Out of the way
More specific:
* Finalized (if it refers to a process)
* Delivered (if it refers to a product)
* Completed (if it refers to a task)
* Finished (if it refers to an action)
The best word to use will depend on the specific situation and the desired tone.