JOSM/Plugins

Installation

With versions greater than 277, you can easily install plugins from within JOSM.

Start JOSM, open the preferences window (Edit->Preferences) and select the plugins tab.
Click on "Get more plugins" to download the list of available plugins.
Check the plugins you want installed.
Click the accept button. All new plugins should start downloading and installing.
Restart JOSM.

With older versions, you have to install the plugins manually.

Download the plugin file from wherever the plugin is hosted. Look in the plugin page or the 'Plugins' page on the JOSM wiki site for the location of this file.
The file should have an ".jar" extension. If it doesn't, rename the downloaded file so that it ends with ".jar". Internet Explorer, for instance, may rename some files to ".zip".
Move the .jar file to the JOSM preferences directory ("%APPDATA%/JOSM" in windows, "~/.josm/plugins/" in Unix/MacOS.)
Start JOSM, open the preferences window (Edit->Preferences) and select the plugins tab.
Activate the plugin in the plugins tab.
Restart JOSM.

Here is a list of available JOSM plugins:

AgPifoJ - Another geotag plugin for JOSM
ImageWayPoint - Photo-mapping plugin for non-geotagged images
Lakewalker - Allows automated tracing of landsat imagery to find water and coastline
LiveGPS - Supports live GPS input ("moving dot") through a connection to "gpsd"
Name Finder - use a third-party name finding service to display an extra tab in the download dialog
Nearclick - useful for tablets and slippery mice, corrects for problem where a click has to have mouse down and mouse up in exactly the same place for a click to work
RemoteControl - Remote control JOSM
slippy_map_chooser - Select the download area on the slippy map
SlippyMap - Displays a slippy map grid in JOSM. Can load tiles from slippy map as background and request updates.
Surveyor - use gps data to set nodes or waypoints at the current position.
Validator - Validates and fixes wrong data.
WMSPlugin - show Landsat or other WMS images (including Metacarta Map Rectifier) in the background
YWMS - Yahoo imagery for JOSM.