Not a major tool, but I'm finding this handy. I often use a cheap chisel for various clean ups - scraping glue, trimming whiskers, easing an edge. Some times the chisel handle would get in the way when working in the middle of a panel, or when trying to keep the chisel flat to prevent gouging the surface. This flush plane does the job and makes this clean ups quicker with less chance of gouging.
This is nothing more than a chisel blade minus the handle so it can ride flat along the surface. I got the idea from a tool catalog, and said 'I can make one of those'. The lucky bit was having a set of cheap chisels that were simply flat pieces of steel with a molded on handle, not the typical form. It was simple to hack saw off the handle. An old plane iron (block plane) would work as well or better.
Has you can see from the pictures, the handle is simply a scrape piece of poplar with 1) a groove routed to accept the blade, and 2) a couple of magnets glued into the handle to hold the blade. The routed groove isn't as deep as the blades thickness, so the blade can ride right on the surface to be cleaned up. In use the tang bears against the back of the groove to react the planing forces. To store the plane, pull the blade out, flip it over and put it back in the handle, with the edge at the back of the groove.
This has been working well for me and it was quick and easy to make.