All shared tools u can find to create .unr maps for l2 (lobbies, zones, etc.).
Prelude -> Prelude dll editor. Works good except terrain editor, but you can create it with different editors.
Interlude -> Unfinished Interlude dll editor.
L2Editor -> Universal client editor, supports all clients till fafurion. Some functions don't work. Breaks level light upon saving the map.
MAPS Unreal Engine -> decompiled Unreal maps so u can modify and import actors from there. Even these which are not supported by your editor.
UedTexKit -> allows to convert unrealG16 .bmp heightmaps to G16 .tiff and backwards.
Geobuilder - creates geodata with client. U can setup startup map in l2.ini.
PandasBuildConv -> converts client-builded geodata into _conv.dat
HDGE -> geodata editor/converter