RetroMMO Online Checker is a free Chrome extension developed by pdxdevchristian. It falls under the category of Browsers and specifically the subcategory of Add-ons & Tools.

The main purpose of this extension is to display the list of users who are currently online on RetroMMO, along with their respective ranks. This feature provides users with a quick and convenient way to see who else is active on the platform at any given time.

Additionally, the RetroMMO Online Checker extension offers the functionality to launch RetroMMO directly by clicking the "Play Game" button. This streamlines the process of accessing the game, saving users time and effort.

Overall, RetroMMO Online Checker is a useful tool for RetroMMO players who want to stay updated on the online presence of other users and easily launch the game.