I have been thinking about writing my own journaling app for years. Not because there aren't good apps in the market, but this is something I want to do. Here are the major requirements:

1. I should be able to write the day's event on there. (There should be a calendar.)
2. It should support encryption.
3. Has a section for notes about people. (Will be useful for keeping track of birthdays, gift ideas, etc.)
4. Has an idea section. (Will use this if I want to work on a new project.)
5. Should be able to embed images (and videos later on.) These images should be a part of the file itself, although support should also be there for referencing images in the file system/by a uri.
6. The editing window should be WYSIWYG, in markdown.
7. Tags for entries should be there. I should be able to search by tags.
8. I should have the option to back it up with my cloud.
9. Search functionality should be there. Search should have filters. (Likeby date, or sections)
10. Create TODOs, on which I can set reminder functionality. (Remind 1 day/1 week/1 month before)

I used to use Lifeograph, so many of the requirements are similar to that one. It was neat and clean.

This is an ambitious project. For now, I have experience using GTK, and some experience using Qt. I think I will go with Qt, since I also want it to be cross-platform. (Plus, I really want to work with QtCreator as well.)