Ask HN: What is one app you can't live without?

I live and breathe LoseIt! (http://www.loseit.com)

I've been logging my caloric intake since 2009. Logging my food keeps me accountable for what I eat and forces me not to eat so mindlessly and without knowing what I put into my body. While I don't usually go back 3 months from now to figure out what I ate or whatever, in the long run, I am able to use the long-term data to understand my eating habits vs. my weight and BMI.

1Password (or other password managers)

My own app! Responding to user feedback and hearing from people who like it reminds me that I've helped at least one person. It provides just enough sanity.

Gmail and Google Maps. Everything else is cheesecake (not even a vitamin)

ssh and a web browser. I know that's two.

I can't live without slack for sure.

tmux is pretty handy for keeping a long-running session open on a server for development work.