vlock is a program to lock one or more sessions on the Linux console. This is especially useful for Linux machines which have multiple users with access to the console. One user may lock his or her session(s) while still allowing other users to use the system on other virtual consoles. If desired, the entire console may be locked and virtual console switching disabled.
vmm is an easy-to-use and configurable commandline tool for administrators and postmasters, used to manage domains, alias-domains, accounts, and relocated mail users. It allows fast and easy management of mail servers. It's designed for installations using Dovecot and Postfix with a PostgreSQL backend.
vnStat is a console-based network traffic monitor that keeps a log of hourly, daily, and monthly network traffic for the selected interface(s). It uses the network interface statistics provided by the kernel as information source. This means that vnStat won't actually be sniffing any traffic, and also ensures light use of system resources.
vncssld is a VNC SSL repeater for Unix. You can use it to access your user's desktop using VNC SSL. The advantage of using a repeater is that you don't need to configure your firewall to be able to connect to your user's desktop: both VNC server and VNC client connect to the repeater. Since it is using SSL, It can even work using a standard HTTP/HTTPS proxy (like squid or DansGuardian).