We present the design and implementation of OCALA, an Overlay Convergence Architecture for Legacy Applications. Unlike previous efforts, OCALA allows users to access different overlays simultaneously, as well as hosts in different overlays to communicate with each other. In addition, OCALA reduces the implementation burden on the overlay developers, by factoring out the functions commonly required to support legacy applications, such as tapping legacy traffic, authentication and encryption. Our implementation of OCALA as a proxy requires no changes to the applications or operating systems. We currently support two overlays, i3 and RON, on Linux and Windows XP/2000 platforms. We (and a few other research groups and end-users) have used the proxy over a eleven-month period with many legacy applications ranging from web browsers to remote desktop applications.