Many developers have read Getting Things Done and turned it into an app in one way or another. Some have have even dared to write programs based on other books despite the overwhelming popularity of GTD. Thinking Rock was the first one that I tried out. When you look at all of them out there on various platforms, both desktop and mobile, there have probably been far too many to list by now. Is this legal or are they just getting away with it?
I would like to produce a mega-app, an integrated productivity environment, that minimalistically implements not only GTD, but as many books on my bookshelf as possible. This covers a broad range of topics: productivity, time-management, motivation, procrastination, brain/mind improvement, etc. I would also like to throw in ideas I get at random from articles, interviews, and other media. Finally, my personal favorite, I would like to implement the major categories of a game I've been addicted to for about twenty years now as a time-management methodology. Very briefly: Growth - exercise, diet, meditation and other related tasks; Science - math (Project Euler, Khan Academy), reading fiction and nonfiction, and other brain improving tasks; Gold - working a job, selling plasma, balancing your checkbook, and other finance-related tasks; Culture - writing, drawing, playing an instrument and other artistic tasks; Production - housework, yardwork, routine work, honey-do's and other high-urgency low-priority tasks; Wonders - projects of high importance: writing a book, writing a program, writing an album, starting a business, building a sculpture, re-building an engine, etc. I call all of this CivLife.
If it makes a difference, I don't intend to profit from it. I would like it to be free/libre/open-source software. Is using the ideas of others like this legal? Would I get away with it? Is it dead in the water? I'm asking because it's an idea that's been stewing in my head for years. I got my BS-IT, but I don't have any experience, so I'm unemployed. I would like to make this program my experience and my life's work, but I don't want it to come back and bite me in the behind.
p.s. If this is the kind of open-ended, debate-stirring, not-beneficial-to-everyone question that gets closed, I apologize and would be happy to refactor it.