Target Weld is a Blender modeling add-on that merges vertices and edges. You work interactively in the 3D viewport, picking a source and a target, while real-time visual feedback highlights the components being merged.
The add-on supports both vertex and edge merge modes, with configurable behavior set to press-only or click-drag. It's accessible through the View3D Tools panel and requires no special permissions.
Target Weld is listed here as free, and the author can be supported by buying their other add-ons from Superhive. It's compatible with Blender 4.2 LTS and newer, and released under the GNU General Public License v3.0 or later. Version 1.1.9 landed a typo fix. Issues can be reported through the developer's Discord, and the add-on appears in the Blender Extensions library.