Texifier allows you to open files in your projects in multiple tabs. Note that the tabs are designed to open different files of the same project, but not different projects. A project here refers to an input file or a set of input files containing LaTeX source that compile into a single output PDF.
Tabs in a window may have different editor and PDF locations, allowing you to work on different parts of the project simultaneously and easily switch between them. You can create as many tabs as you want.
Creating a new tab (