The Real Estate Standards Organization (RESO) has set its goals to produce a common language spoken by systems that handle real estate information, such as multiple listing services (MLS). A common language enables computers like the one on your desk to receive information from many different real estate systems or MLSs without being specially "trained" to understand the information from each.
Standards like the Data Dictionary, Web API and RETS 1.8 exist in many different industries. For example, air traffic controllers at international airports all speak English, no matter what their native language, so pilots are guaranteed that they need learn only one language to fly anywhere in the world.
The RESO standards is a language that was built for a specific purpose: to have all computers that deal with real estate information "speak" the same language, so that you can use the same desktop computer program with any MLS that has adopted RETS.
For software developers and providers of services like IDX sites, web portals and Broker in-house systems RESO Standards means having to write programs to use only one language in order to work with many different systems. This means lower costs, more products, more competition among vendors, and faster implementations of new systems, all of which directly benefit people who work with real estate information as a living.
For a more comprehensive overview please review the documents below.
RESO Data Dictionary
RESO Web API
RESO Application Interoperability Best Practices Guide (open for comment)
RETS 1x tools libRETS and ezRETS support sites.