Mason is a tool that interactively builds a firewall using Linux' ipfwadm or ipchains firewalling. You leave mason running on the firewall machine while you are making all the kinds of connections that you want the firewall to support (and want it to block). Mason gives you a list of firewall rules that exactly allow and block those connections. It can either build a firewall from scratch for you or supplement an existing firewall.
Isinglass is a firewall setup script designed to protect dial-up users. It protects a user's system against security holes in programs user may not even know are running. Most users can run it "out of the box" without any configuration required. It will automatically detect network interfaces and IP addresses. isinglass-hzd is an unofficial bugfix/2.2 support release.
vpnd is a daemon which connects two networks on network level either via TCP/IP or a (virtual) leased line attached to a serial interface. All data transfered between the two networks are encrypted using the unpatented free Blowfish encryption algorithm with a key length of up to 576 bits (may be downgraded to a minimum of 0 bits to suit any legal restrictions).
UserIPacct introduces a new policy mechanism that provides per-user IP statistics (measuring the user's IP usage). This package adds per user IP accounting to the Linux kernel, and contains programs to control and use this accounting data. Patches are available for the 2.0.39, 2.2.19, and 2.4.5 kernels.
Dialback is a set of html pages and some bash scripts to enable a host to call you back and set up a ppp link. It also includes a MS Windows dial-up networking script should you wish to use such a machine for a client. It is intended for legitimate remote access where you need good security (ppp link only available on return call) and/or the other end is willing to foot the bill for your connection time. Please note that it should be fairly to set up other protocols such as slip.
The Cistron Radius server is mostly compatible with Livingston's 'radiusd-2.1', except without the s/key or menu support. It has additional features such as multiple DEFAULT entries with fall-through, a session database (who is online), the ability to limit connections on a per-user basis, and much more.
PPTP Client allows you to connect to a PPTP server from a Linux box. It sets up a PPTP call, after which the PPP daemon establishes a PPP link over that PPTP call. The client can access PPTP-based VPNs. Besides remote access to internal corporate networks, some CATV and ADSL ISPs are using PPTP to provide Internet access to their customers.