Libre Hardware Monitor is free software that can monitor the temperature sensors, fan speeds, voltages, load and clock speeds of your computer.

Stack Exchange's Monitoring System

Exceptionless application

App Metrics is an open-source and cross-platform .NET library used to record and report metrics within an application.

.NET library to instrument your code with Prometheus metrics

WatchDog is a Realtime Message, Event, HTTP (Request & Response) and Exception logger and viewer for ASP.Net Core Web Apps and APIs. It allows developers log and view messages, events, http requests made to their web application and also exception caught during runtime in their web applications, all in Realtime.

ApplicationInsights-dotnet

Exposes .NET core runtime metrics (GC, JIT, lock contention, thread pool) using the prometheus-net package

ASP.NET Core web applications monitoring

OPC client made simpler, for UA and DA

FanControl plugin to import HWInfo sensors.

GUI Tool for beginners and experts to Monitor and Analyse Chia Plotting log files, show health and progress of running plots and estimated time to completion. No setup, configuration or installation of python or whatever required. Just install and enjoy.

EasyNetQ.Management.Client is a .NET client for the RabbitMQ RESTful management API

Distributed tracing and stats collecting framework

Microsoft Application Insights for .NET Web Applications

Customizable real-time monitoring for .NET Core services.

A file and folder monitor that can send notifications, perform actions, or execute a command when a file or folder is changed.

PSEventViewer (Get-Events) is really useful PowerShell wrapper around Get-WinEvent. One of the features you may be interested in is a simple way of getting “hidden” events data

.NET Logging adaptors

Benchmarking and monitoring automation, designed for cloud, built with .NET.