Kerbal Mars Program
While many automated space missions visited all the different places in the Solar System, Moon remains the most distant place a man has stepped his foot on. NASA Constellation Program aimed to extend the reach of human spaceflight to more distant objects, including Mars. A lot of different missions were proposed and one of the approaches planned to use 7 launches from Earth with further docking in Earth and Mars orbits. That would allow to deliver some of the cargo separately from the crew and to produce some of the fuel for the return journey. The planned duration of crew's stay on Mars was almost 2 years. However, none of those came to pass, as the financing of NASA was constantly cut.
What USA cannot do, Kerbin can. After the support for multiple missions and docking was added to Kerbal Space Program, the players' community looked forward to replicating Constellation missions in the game. A month ago, KSP player and modder katateochi has demonstrated his amazing replication of the proposed Mars mission. He has modded KSP to add parts based on NASA designs and constructed a complex mission from Kerbin to Duna (KSP's versions of Earth and Mars). It is an amazing thing to see, looking even more exciting that original NASA concept video. KSP's setting and joyful Kerbal astronauts add some fun to it as well.
While KSP's proof of concept is never enough for real life, the enthusiasm it brings for manned space exploration is a good thing nevertheless. Maybe we will live to see something like this not in the computer game, but on live broadcast.