It's simply an an ultra-simplified one destination email client.
One button on your homescreen opens up a little text input window. Hit send, and it emails yourself. That's it, and it has been absolutely life changing, I've retained so much and simplified so many things. Ideas, scheduling, notes, etc.
Then about once a month I copy paste the whole chat into a text file on my workstation PC, date and archive it, and clear the chat. Telegram includes the exact time and date of each message in the paste, and my consistent "tagging" of the notes with the topic means that I can programmatically parse the text files later to organize them, maybe on my website.
After years of note-taking in various forms, I find that I rarely actually need to peruse my notes archive. It's the act of taking notes itself which helps with retention of ideas.
Most everything else in my life organization-wise, I use http://zim-wiki.org for. I just go through them and file them in ideas or todos.
I try to avoid using my phone as much as possible. The rule of thumb there is -- if it's not a real human communicating to me directly/individually or as part of a small group, I should try to just use the computer or not use it at all.