The Business Manager is a web application which helps keep track of your in-game business supply and stock levels in GTA Online. It simulates the businesses and notifies you when one needs your attention.
To begin, click the cog of a business tab to set it up. Product and supply bars can be set by dragging the bars to their in game values. Then, whenever you are in a session where businesses run (such as free roam and contact missions), start the manager using the button near the map. Pause it when you are no longer in a session. Your information will persist between browsing sessions.
You can install the Business Manager through browsers that support Progressive Web Applications (PWAs) for a more native application experience. Currently, most mobile browsers support PWAs, as well as some Chromium-based desktop browsers. The option to do this is generally found in your browser's dropdown menu.
Version history is documented in the patch notes section of the web application.
func_vehicle
Flopster - Mobile layout fixes
sol3uk - Dark mode
benaw - Nightclub vehicle requirement, favicon, device sleeping fixes
juanminm - Toggleable business upgrades, Nightclub storage floors
Arsonide - Acid lab