Join the most popular Internet of Things platform with free Cloud, iOS and Android mobile apps, Web dashboard, and Machine Learning. Has mobile apps for interacting with interfaced devices. Assemble custom apps with a drag-and-drop builder. If it's networked and you can mess with it, you can get it talking to Blynk.
If you want to use their service, developer accounts are free but are limited to five (5) devices at a time. Paid service starts at $415us.
Open source: You can download the server's source code and run it yourself if you want. It's written in Java.
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