I’ve been using a tool called http://dmpr.io/ for a couple of months to store everything of GTD’s Someday/Maybe type in my head.
The tool helps me to free my brain of these things. At the same time, the tool will bug me with the things I store in there from time to time so I know they won’t be forgotten.
I use it for all kinds of things: business ideas to look into further, stuff to do some research on, recipes to try out, books to read, etc.
Are there any other tools out there that can be used to that end? Are there any mobile apps?