Rob's script is called Where in OF, and can be found here
. A search for "projects where number of available tasks > 0" would show you all projects that have available tasks, including those on hold, in dropped folders, etc. A more tailored search would be "projects where (((status is active) and ((effectively hidden of its folder is false) or (its folder is missing value))) and (number of available tasks > 0))" which is quite a handful to type. Fortunately, the script allows you to build a library of custom searches, and has an abbreviation facility as well so that you could search for "projects where ([Active] and (number of available tasks > 0))". I just reported a bug to Rob that prevents that last abbreviated search from working properly, but no doubt he'll have a fix shortly, and the other searches I mentioned will work in the meantime.
When you run the script, it makes you a window that focuses on the projects that match the search query, so the others are completely hidden from view, even if you switch to context view. However, if you complete enough tasks to make some of the projects no longer eligible to be in the view, they will still remain until you run the search again — it doesn't update dynamically.
It's a great script, and I think the only days where I don't use it are the days where I don't use OmniFocus on the Mac!