It's a log, not a daily one. I use pieces of paper. Started with various wikis, org, markdown, text file, email. Refined and refined it to the bare minimum. Came a point where all I needed was some random piece of paper and something to write with.

My end goal is to not even need these. But I haven't met anyone that at that level and I don't see a way to get there.

One key insight - its not about writing things. Its about reading them and re-reading them.