Realm is a mobile database: a replacement for SQLite & Core Data. It can save you thousands of lines of code and weeks of work, and lets you craft amazing new user experiences.
Realm is not built on SQLite. Instead, a custom C++ core is used to provide memory-efficient access to your data by using Realm objects, which usually consume less RAM than native objects. Its data structures look like the Objects and Arrays of your language, but provide additional features such as: querying, relationships & graphs, thread safety, and more.