Really? No mention to any PC TBSs so far?
Come on! The original roots of PC multiplayer was the good 'ole Hot Seat! I'm ashamed of you so-proclaimed "PC Gamers"...
I can't say for sure, but I think the last TBSs released were Civilization 4 and Heroes of Might and Magic 5, both allow hotseat, that is, play one turn then leave the seat for your friend (and thus, why it is called "hot seat"). Galactic Civilizations 2 may allow, but I'll have to get back to you because I never tried. Civilization 5 will probably allow it, as should Disciples 3. The revered Lords of Magic also allows it, but it is a bit funky to get it going. Pretty much all Turn Based Strategy games that are all resolved in turns have hot seat.
My infancy was spent playing Heroes of Might and Magic 2 in hotseat with my brother. Geez.
That is not dead
Which can eternal lie,
And with strange aeons
Even Death may die