I'm working with Microsoft Project.
If I'm interpreting properly your question, you want to get several projects using same resource pool.
So, at first, you need to create a resource pool (there's plenty of information how to do it either in the Microsoft Project web, or even in this fórum - I didn't check in deep however - ).
If you want to limit the resource usage for a Project, the only possibility I see is to assign multiple names to a single resource in time-slots (e.g. Resource_1_Slot1, Resource_1_Slot2, etc...). Each time slot can be assigned to a fraction of the resource (e,g 2h, 4h, etc...).
So, if some of the slots is already planned, a conflict (red man) will appear & you can realise & use different slot.
Drawback is that you need to properly define time slots for a single resource in different names, & utilization efficiency of every resource in total is difficult to monitor. However, for the different projects, is posible to be aware of resources constraints.
Hope it helps.