Dante is a free implementation of the proxy protocols SOCKS version 4 and SOCKS version 5 (RFC 1928) that supports both IPv4 and IPv6. It can be used as a firewall between networks and to control outgoing or incoming traffic. The package consists of two parts: a SOCKS server and a proxy client that supports SOCKS, HTTP proxies, and UPnP. RFC 1961 (GSSAPI) is supported in both the client and the server. Commercial support is available.
Burd's Proxy Searcher is a Windows GUI to easily uncover public and free-to-use or anonymizing proxy servers. It's based on a customizable and filterable search engine, and automatically probes result lists for server accessibility. It can test for HTTP or SOCKS proxies, and instantly apply settings to the current web browser.