My most used tool I have is a note taking web app that automatically saves markdown files to S3. The most important feature I added was a little button that would automatically make a note for the current day, and put it in the daily notes folder, all sorted and organized. I also have full text search which is very helpful for finding old notes.

I also use an RSS reader I made. Instead of just showing you the text of the page like a standard RSS reader, it proxies the web page so you can read the article directly from the website, but with the added benefit that since it's a proxy, I can control all the HTML, CSS, and Javascript on that page.

Another daily one I use is a random background music playlist for Spotify that is auto generated daily. Using the Spotify API you can find random music, then find random instrumental music from that random music. I use this to discover new songs to listen to while working.

Basically, making your own software is fun. Making production software is much less fun. I don't need to worry about a million things when I make my own software. Sure, I make $0, but if I spent months making, for example, my notes app production ready, and tried marketing it, I'm guessing I'd still be sitting at $0.