Speaking of JOSM plugins, I've made a few.
This is Relation Toolbox. It reverses how we work with relations: instead of editing relations themselves, we edit an object's membership.
With it, you choose a relation, and then click on nodes and ways (and other relations) to add or remove them from the chosen one.
It also introduced automatic multipolygon construction and de-construction.
https://wiki.openstreetmap.org/wiki/JOSM/Plugins/Relation_Toolbox
Fun fact: my first ever SotM talk (in 2011) was on this plugin.
You know how most imagery is offset, and you need to align it with GPS traces and other stuff before mapping? No? Haha.
My another project from that time was the Imagery Offset Database. A huge list of reference points than helps align imagery automatically. Complete with a JOSM plugin and tons of documentation. Turned eleven last month, still very active.
https://offsets.textual.ru/
iD editor was written by americans with perfect imagery, so it still doesn't support it:
https://github.com/openstreetmap/iD/issues/1124
You know how most imagery is offset, and you need to align it with GPS traces and other stuff before mapping? No? Haha.
My another project from that time was the Imagery Offset Database. A huge list of reference points than helps align imagery automatically. Complete with a JOSM plugin and tons of documentation. Turned eleven last month, still very active.