SQLite is made to be extremely lightweight and portable, but it still uses SQL. However, some SQL features such as RIGHT OUTER JOIN and FOR EACH STATEMENT are missing.
SQLite has bindings for a large number of programming languages, including BASIC, Delphi, C, C#, C++, Clipper//Harbour, Common Lisp, Curl, D, Free Pascal, Haskell, Java, JavaScript, Livecode, Lua, newLisp, Objective-C (on OS X and iOS), OCaml, Perl, PHP, Pike, PureBasic, Python, R, REALbasic, REBOL, Ruby, Scheme, Smalltalk, Tcl, Visual Basic.
An SQLite database is a single ordinary disk file that can be located anywhere in the directory hierarchy. It works by sending requests to a single file where all the data is kept instead of communicating with a hosted database which gives access to an interface by making use of sockets and ports. The file format used is also cross-platform, so can easily be migrated to various machines.
This makes SQLite extremely portable throughout different applications, all that's needed to transfer the whole database is to make a copy of the file.
Because of it's ability to scale and with the portability that a single-file database gives you without losing much of the power and features that SQL gives developers, it's a great choice for testing applications and for the early stages of development when the workload and the data that needs to be stored is not that large.
There is literally no configuration required to get SQL lite up and running. This is mainly due to SQLite being serverless, there is no separate server process to install, setup, configure, initialize, manage, and troubleshoot.
It's a very unfortunate thing, but it's true. Not many people know of this gem so that makes it difficult to find community support at times. It also makes it hard to get people on board with it who shop products by brand name or flashy marketing. It also means there are fewer code snippets, libraries, and frameworks that consider it. While it's interoperability is good with SQL support and Tinkerpop, it still doesn't change the fact that many things don't give it much thought and that can lead to more work as a developer sometimes.
Unlike other NoSql databases, OrientDB offers clustering support for free. Furthermore, it's not a basic Master/Slave, but it supports Master-Master replication + Sharding.
This database is primarily, or historically, thought of as a graph database. However, it is actually a multi-model database that supports a variety of noSQL models (key-value, document, etc.).
The Community Edition is free and covers many features, but an Enterprise Edition is available (prices are transparent, published online) with 24x7 support.
A lot of effort went into making OrientDB easy and familiar to use (such as SQL queries for example). However, it's important to understand the database engine a bit and how it works in general (links for example). This involves a bit of a learning curve if you're not familiar with graph databases. Not an enormous curve or anything, but it's still a consideration.