CTP 2.1 is available for SQL Server 2016 to evaluate for 180 days.
Download SQL Server 2016
You’ll need to log in with a Microsoft account. You can download a CAB to install the program, and ISO file to burn to DVD, or run in Azure.

SQL Server 2016 Datasheet
MSDN – What’s New In SQL Server 2016
SQL Server Central – Learning SQL Serve 2016

Installation Requirements:
You’ll need to be on Windows 8 or Windows 2012 R2 (or later editions) to install 2016. You’ll need the .Net Framework 3.5 SP1 or later and 6 GB of disk space.

New Features:
Here are some of the new features in the new edition:

Masking columns: Standard and custom masks to apply to data in query results, to keep users from viewing sensitive data, like credit card numbers or SSNs.
Polybase: SQL layer for Hadoop and Azure Blob storage
Multiple TempDB files: You’re allowed to set the number of TempDB files, with the default being the number of cores in use, up to 8. Aaron Bertrand on 2016 TempDB
Temporal tables: Auditing data with the ability to query to see the data at a specific point in time.
In-Memory Tables: Now supports tables up to 2 TB (from 256 MB in 2014), support for constraints.
Always Encrypted: Data is encrypted on disk, in memory and in transit without making application changes. Encrypted data can be Randomized or Deterministic(where the same value will hash to the same value).
Query Store: Stores history of execution plans.
R Programming Language support in the database.
Row Level Security: Hide certain rows for specified users.
Stretch Databases: The ability to archive data to Azure, but still access it in SQL Server queries without any changes.
JSON: Format query results as JSON, much like XML.

I’ll follow up in the coming weeks with more detailed posts on some of these features.
SQL Server 2016 – Temporal Tables
SQL Server 2016 – Data Masking
Row Level Security
JSON Support