Idea Summary
At this time it does not seem possible to model parallel executions in APEX workflow.
In Flows for APEX parallel gateways are used to enable multiple activities in parallel and then wait for all parallel paths to be completed before continuing with further activities.
Use Case
Any time, when more than one activity could be performed in parallel (e.g. 2 approvals or actions by different roles).
Preferred Solution (Optional)
The model could be designed using parallel gateways as in Flows for APEX.