A BizTalk Accelerator is an industry specific solution and there are two editions:  Enterprise and Standard.  Each edition is installed with the corresponding BizTalk Server edition except for Developer edition which requires Enterprise.  Each accelerator has a specific installation guide and must be followed after the core BizTalk Server is properly installed and configured.  BizTalk Server 2010 has the following accelerators:

The accelerators do not have to downloaded separately as there are integrated with the BizTalk Server ISO (Standard and Enterprise Edition).

BizTalk Accelerator for SWIFT (A4SWIFT)

This accelerator provides a set of schemas, rules, and associated tools to assist you in the integration of SWIFT messaging with your internal applications.  Along with A4SWIFT or by itself, you can also use FileAct and InterAct Adapters which provide connectivity between BizTalk Server and the SWIFT Secure IP Network (SIPN) for the transfer of files. 

SWIFT guidelines are issued once a year and in order to implement them, Microsoft issues a Message Pack yearly.  The latest being for BizTalk Server 2010 is Message Pack 2010

BizTalk Accelerator for HL7 (BTAHL7)

This accelerator allows you to develop business processes between your health care computer systems. By using BTAHL7, developers, IT professionals, and interface analysts can work in a common environment to develop end-to-end integrated BTAHL7-based solutions across health care applications.

BizTalk Accelerator for RosettaNet (BTARN)

Streamlines the development and deployment of RosettaNet standards-based integration solutions.  BTARN supports the RosettaNet Implementation Framework (RNIF) versions 1.1 and 2.0.01. RNIF is an open network application framework that enables business partners to collaboratively run RosettaNet Partner Interface Processes (PIPs).

See Also

You can also read the following about accelerators:

Another important place to find an extensive amount of BizTalk related articles is the TechNet Wiki itself. The best entry point is BizTalk Server Resources on the TechNet Wiki.