The Grand Tactical System is a series of company-level games originally designed by Adam Starkweather and published by MMP. MMP is still developing further games in the series, while Starkweather has developed a slightly simpler series, the Company Scale Series, which being publshed by Compass Games.

GTS games tend to be huge packages (with one exception), and concentrate on the ability of division HQ to coordinate the activities of their sub-units (which is probably why the games tend to be huge).

I have not tried the CSS games yet, but the individual games are more varied in scope.

After Action Reports:

No Question of Attack

Links:

Collection Status
Grand Tactical Series
No Question of Surrender	Operation Mercury