Modern Tron, or Urzatron, is a deck that runs off of the three "Urza" lands (Urza's Mine, Urza's Power Plant and Urza's Tower) in order to make large amounts of mana. There are a number of different kinds of such decks in the format; this article will detail the most common variants.
RG Tron, once the most popular archetype, is a Green-based Urzatron deck that frequently splashed for Red in order to gain removal. In terms of assembling Urzatron, it is the fastest and most consistent Urzatron deck in the format, playing a plethora of cantrips and tutors to do so, allowing it to land powerful cards such as Karn Liberated as early as turn 3. Its drawback is that it is far more reliant on assembling Urzatron than the other decks, and thus is set back significantly more by disruption such as land destruction. As Modern developed, the power of two-damage sweepers was weakened and Walking Ballista was printed, giving Tron a secondary payoff and superior defensive option. Most Tron decks now eschew Red, adding Relic of Progenitus as a better disruptive piece and ignoring aggressive matchups entirely.
Gifts Tron, also known as UW Tron, uses Gifts Ungiven, Expedition Map or Realms Uncharted to tutor for the lands. The deck is pretty straightforward: assemble the combo pieces, use removal and permission as necessary, and ramp into game ending threats. More common during the Extended era, the deck fell out of favour around 2014, with classic UW control being superior in consistency and had gained more in recent printings, while Gifts Tron and other blue Tron decks having a fairly rigid base.