Are you aware that thinkspeak is opensource already (GitHub - iobridge/thingspeak: ThingSpeak is an open source “Internet of Things” application and API to store and retrieve data from things using HTTP over the Internet or via a Local Area Network. With ThingSpeak, you can create sensor logging applications, location tracking applications, and a social network of things with status updates.)?
Alternatively Home - Nim_bit_S also appears to fit your use-case.