Projects have two attributes called Client and Type which you can use to group projects into categories. You can use these properties when filtering your reports and when exporting data.
On NikaTime's Report Center
When creating a new project on the Projects Management page, in the dialogue box, select from the list or write the name of the Client or Type. When you write a new value, you can create a new client or type by clicking the new name on the list.
You can edit the name of the clients or the project types by clicking the Clients or Project Types buttons on the top-right corner of the Projects Management page.
In the same way that you create types and clients by associating them with a project, to delete types or clients, you have to remove them from all projects associated with them.