Current virtual reality (VR) systems limit users to a single virtual 3D environment (VE) at a time, which restricts their ability to engage with multiple VEs simultaneously. We present SLIVR, a VR-Hub designed to enhance multitasking capabilities by arranging multiple VEs in a regular polygon formation around the user. Each VE is visually represented by life-sized 2D previews that facilitate hub-based interactions. Direct Selection enables users to select objects within a VE directly from the preview, allowing them to remain within the hub. Additionally, Focus-mode enlarges a chosen 2D preview, providing access to objects beyond the initial viewport. In a user study ($\mathrm{N}=18$), we evaluated SLIVR against a conventional grid-based VR app launcher and a hub that utilized SLIVR's visualization but only supported Teleportation interactions. Our findings revealed that SLIVR improved target selection performance by 16.8% overall and by 30.5% when engaging with six VEs, compared to the grid-based app launcher. Notably, hub-based interactions accounted for 94.9% of selections, with Focus-mode being utilized six times more frequently than Teleportation.