Gizmo5 has launched a web-based VoIP app that allows users to call 800 numbers and SIP addresses for free.
GizmoCall is Flash-based, so it only requires a browser to use the service rather than having to download a software client.
Users go to the Web site, sign up for a username and password, and start making calls.
The service can also accept inbound calls to the login user name, so long as the app is running in a window or browser tab.
You can also drop one line onto a webpage to do inbound calling from GizmoCall.
To make outbound calls, users require a GizmoCall account.
The Adobe Flash client should work on Mac, Windows and Linux platforms.