In Eclipse, you can use Workspaces and Working Sets to keep relevant projects separated, NetBeans does not have Workspaces, but it does have an equivalant to the Working Sets from Eclipse.
If you have many projects in NetBeans, and struggle to keep an overview, like I did, then you may want to look into Project Groups.
Project Groups in NetBeans is a simple and easy way to only have open the projects you need at the moment, and hide the other non-relevant projects from sight.
To create a Project Group, right click in the Projects panel, choose Project Group and then New Group, like pictured below.
You can then give your new group a name, and specify which projects should go into the group.
If you choose Free group, and Use currently Open Projects, Netbeans will create a new group with the same projects that you currently have open.
If you create, say, 2 groups, one for work, and one for school related projects, you can just right click a project (or several projects at a time) in the work related group and click Close, to close the project. It will be closed (and thus out of sight) in the work group, but open in the school group.
Also, if you have many projects in a separate directory, you can choose the third option, Folder of Projects, to make a group from a folder of projects.
When you have created a Project Group, you can just right click in the Projects panel and choose your Group from the Project Group menu. Easy!