The best free alternative to Thinfinity VirtualUI is Zero Install, which is both free and Open Source. If that doesn't suit you, our users have ranked seven alternatives to Thinfinity VirtualUI and four of them is free so hopefully you can find a suitable replacement. Other interesting free alternatives to Thinfinity VirtualUI are Enigma Virtual Box (Freemium), rollApp (Freemium) and Thincast (Free, Open Source).
Zero Install is a decentralised cross-distribution software installation system. Other features include full support for shared libraries, sharing between users, and integration with native platform package managers.