Telegram + dynamist
Every time I have an idea, I send a message to myself using telegram: there is actually a widget just for that in android.
It's awesome cause you can type, take a a picture or a video, dictate... And it syncs across devices, giving you access anywhere to a timeline of your thoughts.
Then when I got time I pop the stack and sort in as projects into the wonderful dynamist. It works offline, on Linux and mobile, syncs, allows notes and nested todo.