WadAuthor is a shareware sector-based level editor written by John Williston. It is still somewhat popular because of the extendability functions provided by its WCF files, even though the editor itself has not been updated for several years.
Rather than drawing lines to create sectors, WadAuthor has two options to insert new sectors, New Rectangular Sector and New Polygonal Sector. Rectangular sectors default to the grid setting being used, so if the standard 64x64 grid is being used, it will create a 64x64 square sector. The smallest grid setting is 2x2 and increases in multiples of two up to 1024x1024. A custom horizontal and vertical length can be specified if the user prefers. Adding a polygonal sector will prompt the user to enter the number of sides and the desired radius. To add more sides to an existing sector, a linedef can be split into two. New sectors placed inside existing sectors will automatically inherit the properties of that sector, with the exception of tags.
The user can highlight and select any map object, vertex, linedef, sector or thing, without the need to be in a specific mode. There is a filter option to only select a particular type of object, say for example, linedefs, but the user can still create sectors whilst their object selection is filtered.