https://bitwisecmd.com is a web-based bitwise calculation tool. Its main goal is to help people understand how bitwise operaiton works by presenting numbers and operation results in binary format.
I initially created a tool in 2012 to help me better understand how Flags enums work in C#. I've decided to share it with everyone by converting it into the web application in 2015. And of course I couldn't resist the temptation to write my own JavaScript framework similar to Angular JS. I released the first version after 4 days of working from home while being on a sick live and having a mild feaver. It had templating engine and DI container. Since then I rewrote it in React because suprise-suprise supporting framework that you wrote yourself is not as easy as one might think. Espcially if you return to it after long pause. Still, I regret nothig. You can see here and here how application looked like back then (spoiler: very similar to AngularJS).
After some time I got into learning about networking in AWS. I needed to understand how IP subnet masks and CIDR notations work. Again, it was about bitwise operations. So I've extended BitwiseCmd with additional commands such as subnet, vpc, and support of IP address inputs.