Simply put, echoWare enables any peer-to-peer or client-server
application to utilize a "packet relay server" approach in order to
achieve end-to-end connectivity without adjusting any intervening
firewalls or NAT'ing routers. Many remote access applications
have a "packet relay server" capability to them (e.g, GoToMyPC,
GoToAssist, and others), but echoWare is the first software
package we know of that allows any Internet application to quickly
and easily incorporate this capability.

You can download the echoWare SDK for Windows here:

ftp://ftp.echogent.com/EchoWare

The echoWare DLL is open-source, and is available under the
"Sleepycat license". This license permits you to use echoWare at no
charge under the condition that if you use the software in an
application you redistribute, the complete source code for your
application must be available and freely redistributable under reasonable
conditions. If you do not want to release the source code for your
application, you may purchase a license from Echogent Systems.
For pricing information, or if you have further questions on
licensing, please contact us.