Countdown Timer 2

I would like to build an app that counts downward by days. (i.e. Day 20, Day 19, Day 18...) This would be a stand alone app that can be used on a desktop, smartphone or tablet. (Windows or Mac) I would like the app to be generic so that a USER could enter the following data: 1) the number of days desired to countdown; 2) the time(s) of day that the countdown action would occur; 3) the action desired such as open a video, song, or text message, etc; 4) an interface that is fairly user friendly such that the average person could enter the info and make it customized for their particular use. Of course the actions could be the same for ALL days OR could be modified where the user could enter a different action for each day. For example, a user could enter data for a 30 day exercise workout routine. The user enters "30 days" exercise program to countdown. The time for each day of the workout. Then, the message (file) pops up each day, at the designated time, reminding the user that they should exercise NOW and a text and/or audio cue would play telling them what they need to do for TODAY'S exercise. I am sure there are apps that do this already but I would like to have an app that I OWN and can design different count down uses for various types of tasks. I would like to give some of the versions for free and sell the more interesting uses that I create therefore, I need to own the complete rights to my software. In other words, I don't want an existing software that you simply modify and then I find out that I don't have the right to use it any way I chose. I hope you understand my concern. If not, please ask for further info. I am familiar with Actionscript 3 and so I know this could be done with Flash, but Flash is no longer cross-platform. So, I am looking for suggestions of the proper type of programming that should be employed to create this app with the features I have stated. I have tagged certain types of talent that should look at this project, but I am NOT saying that the project is limited to those who know these software programming languages. But rather, I am looking for YOU to tell ME what software programming YOU would recommend to make this particular project works correctly.