Kestrel vs Mosquitto: What are the differences?

Kestrel: Simple, distributed message queue system. Kestrel is based on Blaine Cook's "starling" simple, distributed message queue, with added features and bulletproofing, as well as the scalability offered by actors and the JVM; Mosquitto: An open source message broker that implements the MQTT protocol. It is lightweight and is suitable for use on all devices from low power single board computers to full servers.. The MQTT protocol provides a lightweight method of carrying out messaging using a publish/subscribe model. This makes it suitable for Internet of Things messaging such as with low power sensors or mobile devices such as phones, embedded computers or microcontrollers.

Kestrel and Mosquitto can be primarily classified as "Message Queue" tools.

Kestrel is an open source tool with 2.8K GitHub stars and 326 GitHub forks. Here's a link to Kestrel's open source repository on GitHub.