ASSETS
About
I wrote Runtime Monitoring so I could see the state of my own C# classes and objects while a game was running. Add the 'Monitor' attribute to a field, property or event and its value or state shows up in a UI that can be customized and extended. It comes from a time when there was no straightforward way to do this in Unity, and building it was also an exercise to get better at C#. It is free and open source and the code is there if it is useful to you, but I do not use it or maintain it anymore and I would not particularly recommend adopting it today.
About
I kept writing the same code to move work from a background thread back onto Unity's main thread, so at some point I put it in one place. Thread Dispatcher passes the execution of a Delegate, Coroutine or Task to the main thread and lets the calling thread await its completion or result. It also lets you pick the exact execution cycle the work runs in and cancel pending work with a CancellationToken. Like the other tools here it is free and open source, and like the other tools here I no longer use or maintain it. A lot of what it solved is less of a problem today.
About
Managing scripting define symbols through Unity's project settings was tedious, so I turned them into assets instead. A preprocessor symbol definition file works like an assembly definition file: an object you create in your project to manage custom #defines, also known as preprocessor symbols or scripting define symbols. This is the smallest of the three and the one I built purely for my own workflow. It is free and open source, and it is not maintained.