Simple IoT is designed to work with several other applications for storing time series data and viewing this data in graphs.
InfluxDB is currently the recommended way to store historical data. This database is efficient and can run on embedded platforms like the Raspberry PI as well as desktop and server machines. To connect SIOT to InfluxDB, simply add an InfluxDB node in your setup, and fill in the parameters.
Grafana is a very powerful graphing solution that works well with InfluxDB. Although InfluxDB has its own web interface and graphing capability, generally we find Grafana to be more full featured and easier to use.