MagicpPlan. This handy application allows you to create a floor plan by taking pictures with your Android, iPhone or iPad.
The procedure is straightforward: you stand in one place, slowly turn around and trace the outline of the room. It will automatically scan the dimensions and produce a floor plan, which you can export into a number of different formats (including, PDF, JPEG and DXF, as well as HTML if you want to host it on a website).
You can edit the plan afterwards - adjusting the dimensions, adding objects, including a watermark or scale, etc. - so that it meets your needs.
As a real estate agent, this can be particularly useful. One thing that home shoppers want to see when evaluating a potential property, is a bird's eye view of the layout. Nice, high-quality pictures are great to attract their attention, but a floor plan is something that will retain them.
It was listed among TIME.com's Top 50 iPhone apps of 2013 when first released. Since then, they've released an updated version, incorporating consumer feedback.
They have a basic free version, which allows you to create and share floor plans with other MagicPlan users. However, to get all the other benefits will cost you $9.99 / month.
(The good news is that if you're a RESAAS user, then you can get a further 10% off this price. All you have to is sign up or sign in to www.resaas.com, then click on the three-lined menu in the top right corner and click "Go to Marketplace".)