Mesh Painter is a real-time object placement tool for Blender, developed by Egret Studios LLC. It lets you paint, align, and scatter meshes directly in the viewport, with placement happening in real time as you work.
Built as a Blender add-on, Mesh Painter supports Blender versions 4.0 through 5.1 and is listed as compatible with the Blender extension system. It works with both the Cycles and Eevee render engines and is distributed under the GPL license.
Documentation is included with the add-on, and a demo video is available for a closer look. On the Superhive marketplace, Mesh Painter has recorded 60 or more sales and was published roughly five months ago. This card lists it as free, so check the developer's page for current licensing.