The Outsider Development website (thanks Sector) has the announcement of an OpenGL first-person shooter called Call sign: Charlie set in the Vietnam War that has apparently been in development since 1999, and due for release second quarter 2003. Here's a bit:

The game takes place during the Vietnam War (1964 - 1975). It offers the player full control over a squad of elite soldiers known as Green Berets - specially trained professionals involved in numerous secret missions which took place mostly behind enemy lines. Player can apply his strategic thinking and test his reactions in realistic combat in life-imitating locations. Using a number of authentic weapons, vehicles and aircrafts, mission goals can be accomplished in various ways. Possibility of switching to arbitrary character from the squad whenever the player wants increases the diversity of gaming experience.