Graviteam Tactics series are a real-time realistic wargame featuring mostly WW2 eastern front scenarios. Developed by a small Ukrainian studio, these are amazing games that despite some shortcomings deserve far more success and recognition than they have today.
In addition to the real-time combat layer, the game includes a strategic layer where you can move around units in the large map. When your units meet enemy units you then go to the tactical combat RTS layer.
While this is an RTS game, it is far from a click fest. In reality, when you give orders to an unit, the unit will not necessarily follow them blindly on the spot. It may not even get them if it is too far away from its commanding unit. This is a game that rewards careful planning unlike most other RTS games.
Although the game can look complicated at first, starting to play it is not that difficult. Mastering it, however, is an entirely different matter.
Graviteam Tactics series includes three different games, each with their set of DLC, although GT:OS and GT Mius Front share a couple similar DLCs that have been ported from OS to Mius.
While GT series focuses on the eastern front, both GT:OS and GT:MF have a few DLCs that take place in more recent settings in Afghanistan (1979), China (1969) or Angola (1988). Additionally Tank Warfare is entirely dedicated to the Tunisian Campaign in WW2.
The original GT:OS is based on an older engine and has largely been superseeded by GT:Mius Front. Some content, but not all, from the original GT:OS has been made available in Mius Front. If you find this in a good sale and like the genre, its a good buy.
GT:MF or Mius for short, is a development of GT:OS with better UI, bigger maps and a larger number of units, among several other improvements.
Tank Warfare is not published by Graviteam, but it is developed by them and the engine is mostly the same as Mius Front. It focuses on the WW2 Tunisian Campaign in North Africa.
Graviteam Tactics Boot Camp tutorial videos by Arch Warhammer. A must for any beginner/intermediate player. Although it pertains to the original GT:OS, almost everything is applicable in the newer games.