From the Metal Gear Wiki

Philanthropy is an anti-proliferation group started by Nastasha Romanenko and Otacon, they also recruited Solid Snake to give them a hand. The group is recognized by the UN, or in the words of Snake: "recognized, but still fringe." They mainly wait until information is leaked about Metal Gears and then go and destroy/put a stop to their development. Members:

• Otacon
• Nastasha Romanenko
• Solid Snake
• Mei Ling - this isn't a certainty, but Otacon mentions that she is helping them out by diverting "toys" from the "U.S. Army Soldier Systems Center"

Snake usually carries out the missions solo, with Otacon providing support via codec.

It's also very possible that both Raiden & Rose have joined up with Philanthropy, but evidence is thin. Rose has yet to be seen in footage for MGS4, and Raiden could simply be acting of his own accord just like FOXHOUND. Mei Ling has yet to be heard or shown in any trailer.

[edit] History

[edit] The Forgotten VR Mission

Philanthropy's earliest documented mission. AI Programmer Victoria Reed contacted Otacon and requested the assistance of Philanthropy as a Metal Gear REX was being developed by her company. She had attempted to escape, but was captured. Snake was sent in to rescue her but eventually Snake discovered that Victoria was an AI herself. Snake was actually sent in so that terrorists could infiltrate the facility after he had deactivated the security system of the base. After some time, Snake realized that he was actually in a VR Simulation and that the Otacon he had been talking to was also an AI. The real Otacon managed to contact Snake and attempted to help Snake break free. They both decided it would be a good idea to carry on with the mission, so Snake defeated the terrorist leader, simply calling himself "Commander".

Snake awoke at the end of the mission to the sound of voices. They said that while Snake did prove useful, he failed to provide them with the battle data they needed, and they instruct someone to erase all his memories of the simulation and dump him back where they kidnapped him. However it is unknown whether they erased Otacon's memories as well.

[edit] The Manhattan Incident

Philanthropy's next documented mission was the Tanker Incident of 2007, where Snake infiltrated the tanker Discovery in order to obtain photographic evidence of a new type of Metal Gear - Metal Gear RAY. Philanthropy figured that if they could leak info (along with the photographic evidence) of RAY they could put a stop to its production. However, the info was leaked to them and Snake was caught in a trap by The Patriots. Managing to survive with the help of Otacon, they placed the body of Liquid Snake where the tanker was sinking so people would think Snake died during the incident due to Snake's DNA being practically identical to Liquid's.

Two year's later, Philanthropy came out of hiding when they received information about Arsenal Gear, a gigantic mobile fortress which houses GW, an AI that would filter digital information and remove anything which could potentially harm The Patriots. The AI itself was being developed by Emma Emmerich, Otacon's step-sister. Infiltrating the Big Shell, Snake and Otacon meet up with Raiden and eventually destroy GW, though at the cost of Emma's life.

After the incident, Philanthropy managed to get their hands on a disc which contained a list of all The Patriot's names and whereabouts. One of the names so happened to be the group's biggest financial supporters.