NoSQL is a new type and new concept of database management system.

Below are some of the main differences (of course, there are more points of view) between SQL and NoSQL type database.

SQL type database is also called Structured Data or RDBMS and

NoSQL is called Unstructure Data or Document Database.

Examples of SQL Database - MySQL, PostgreSQL, SQLite
Examples of NoSQL Database - RavenDB, MongoDB, NDatabase

Concept Started Year

SQL- Started in 1970s
NoSQL - Started in 2000s

Figure 1: Numbers of Data handled by SQL and NoSQL Type Database (retrieved from couchbase.com)

The Ability of Handling Large Data

SQL type database will face performance problem when the database becomes large in size.

NoSQL can consistently handle tremendous size of data.

Figure 2: Cost and Performance of SQL and NoSQL Database (retrieved from couchbase.com)

Data Relation Mapping

SQL type - Require data type mapping into .NET, data relationship needs to bind manually.
NoSQL type - No data relationship mapping and binding needed. Whole object is stored directly.

Figure 3: Data Structure of SQL and NoSQL Database (retrieved from couchbase.com)

Schema

SQL - Structure and data types are fixed in advance. To store information about a new data item, the entire database must be altered, during which time the database must be taken offline.
NoSQL - Typically dynamic. Records can add new information on the fly.

Suggested NoSQL Database for .NET

If you are still using SQL type database for years, you can try to move to the Next Generation of Database - NoSQL. You may want to try the following:

RavenDB (.NET)
MongoDB
NHibernate, Examples, NHibernate Membership Providers
NDatabase (.NET)
BrightstarDB (.NET)
LiteDB - Embedded NoSQL database for .NET

Read More

Why NoSQL? - couchbase.com
NoSQL Databases Explained - mongodb.com
10 things you should know about NoSQL databases - techrepublic.com
What is NoSQL? - ravendb.net
NoSQL - Wikipedia

NoSQL - Second Generation Database