GanttProject as a resource planning tool

I am trying to use GanttProject as a resource management/planning tool, and wonder if this is worthwhile exploring.

We have around 25 projects running in our company, and around 10 members of staff. A resource might work on a project for 2 days, then jump to another project, then come back to the previous task in a week or so.

I therefore want to ‘block in’ days when the resource is working on a particular project so I can plan their days for them, and so that they can see what they should be working on.

Is this possible?

I am not sure that I understand what is “block in”.

come back to the previous task in a week or so.

I am not sure that you really meant that, but anyway, resource assignment to some particular task In GanttProject assumes that a resource works on that task from start to the end without interruptions.

e.g. Fred works on 2 projects, Project A and Project B.

He works on Project A on Mon, Tues and Friday
He works on Project B on Wed and Thurs

Would I essentially need to create a new task for Project A to run on Friday?

I assume so.

If anyone could think of something (ideally open source or free) to enable this sort of simple project management, it would be appreciated.

Have you already tried to install and use it? I see no problem in your use case.
A task for each day for each resource. Summary tasks for Project.
Resource view to check overload.
So…?