Ask HN: What are some of your secret development weapons

What are some of your secret development weapons? For instance, before Python became mega-popular (late 90's/early 2000's) it was a tool I used whenever I needed a miracle and it felt like a secret weapon to me since I was the only one in the company using it. What are the secret weapons of today? Those lesser known products/tools (open source or not) that you reach for in a crisis.