D20Pro GM & PC tool complete with Virtual Table Top here: http://www.d20pro.com and HELP here: http://help.mindgene.com/home
I have this program as DM (judge) and 6 guest acounts.

Play Faster

• Quick dice — Easily roll a single dice or combination of dice plus built in support for d20 specific attack, skill, spell damage and save rolls.
• Initiative order — Never ask "Who’s next?" again because all creatures in combat are always kept in order; includes support for readied actions, delaying and custom rules.
• Measure distance — Whether the game grid is in feet, meters or squares the distances on the grid are provided when moving, attacking or surveying.
• Area effect templates — Useful for marking the area of a spell, targeting is built into templates allowing rapid execution of burst, cone, line and custom box templates.
• Combat resolution — Players direct their moves in battle and the Judge is guided through the decision making process for viewing modified rolls, determining hit/miss/crit, and applying damage or other effects.
• Hit point & effect tracking — Damage or healing resulting from attacks and spells or Judge’s discretion is clearly displayed; current effects may be reviewed.

Play Better

• Virtual tabletop — Control your creatures large and small on a grid of any size.
• Maps drawn, tiled, or hi–resolution — Easily switch between multiple maps, each one a creating an immersive game environment.
• Create & import creatures — Create a PC for yourself or build baddies to challenge others; also compatible with creatures exported by award-winning character management software Hero Lab.
• Prepare encounters — Introduce creatures from your Creature Library, tweak, duplicate and arrange them; simply add your players at gametime.
• Manage adventures — Be it in the middle of a 30 round battle or over 30 days as the party treks across a large outdoor map, you will marvel at how the state of the game is tracked during play and completely preserved between sessions.
• Record campaigns — All creature activity is captured by the Game Log, creating a standing history of your adventures; supplemental HTML logs are also generated for easy circulation.

Play Anywhere

• Network multi player — The Judge hosts a game and up to 16 Players may join for cooperative or competitive play.
• Group & private chat — A common chat room is for rules questions or other out–of–character communication; each Player also has a private chat with the Judge.
• Role–playing encouraged — Players may speak, yell, whisper, emote or describe what they are doing in–character.
• Upload creature — If the pregen your Judge provided is not enough, then upload your own PC at gametime from your Creature Library.
• Share maps, creatures, and items — Maps are fully exportable and can be shared with anyone using d20Pro allowing write once, play repeatedly content.

d20Pro 2 is a Java application compatible with Windows, OS X 10.4+ and most flavors of Linux. When starting d20Pro you are able to use the included Guest License, register for a free Trial License, or purchase/upgrade a Player or Full License.

Please download, install, and run d20Pro to connect as a Guest, register for a free trial or purchase a license. Existing account holders may log in to access their licenses at any time inside the program.

Free

The Trial License has all the features available in the Full License except that the trial eventually expires and you must be connected to the Internet each time you start d20Pro during the trial to validate your license. Purchased licenses never expire and do not require an Internet connection.

Guest License

Included

The Guest License comes bundled with d20Pro and allows you to join a game as a Player. The only restriction to this free license is that the Judge running the game must have at least 1 open Guest Slot available at the time you connect. Guest Licenses are included at no extra cost with d20Pro.

Player License

$10

The Player License is similar to the Guest License in that you may only join a game with it. The difference is that you will always be allowed to join a game independent of open Guest Slots. A Player License costs $10 may be upgraded at any time to the basic Full License.

Full License

$30+

The Full License may be used to join OR host a game as a Judge. The basic Full License includes 2 Guest Slots, allowing up to that many Players to connect for free using the Guest License. A Full License costs $30 may be upgraded at any time with additional Guest Slots at a cost of $10 each. Players with their own licenses will not occupy Guest Slots.