Transparent proxying to all hosts/all ports

Hi ! (Please be kind with my poor English...)

Main goal: having ALL connections using Linux TCP/IP stack.

Is there a way to run a fully transparent UDP/TCP proxy on a Linux gateway instead of "just" forwarding packets with Netfilter ?

What I would like to achieve is to intercept all outgoing connections from hosts in the LAN and force Linux to act as a transparent proxy, being the only one "talking" on Internet.

TPROXY (maybe REDIRECT ?) seems to be the right Target for the interception part because SRC/DST host:port are not altered but, correct me if I am wrong, it does only allow to forward packets to one host.

Is there a tool that could inspect incoming packets and, using the Dst addr/Dst port, connect to the right remote host and tranfer only application data ? (HTTP, SMTP, DNS, NTP, etc.)

Thanks !

Philippe