IonDB vs NuoDB: What are the differences?
Developers describe IonDB as "A key-value store for microcontroller and IoT applications". Currently in the Arduino world, there doesn't exist an associative array or map implementation that is both easy to use and performance competitive. There also is little support for disk based storage options that don't involve writing it yourself. IonDB is fast, functional, and offers disk based storage out of the box. On the other hand, NuoDB is detailed as "A scale-out SQL database for global operations". NuoDB’s continuously available, ACID-compliant, SQL database delivers on-demand capacity on commodity hardware across multiple data centers.
IonDB and NuoDB can be categorized as "Databases" tools.
IonDB is an open source tool with 525 GitHub stars and 37 GitHub forks. Here's a link to IonDB's open source repository on GitHub.