They're not especially similar. The Homestead Act of 1962 opened up millions of acres of publicly-held land for private settlement, entirely at the discretion of the settles (provided they complied with the regulations on acreage and so forth). The precise terms of Ti. Gracchus' lex agraria are not certain, but it's quite clear from our texts and from the lex agraria of 111 that it broke up holdings of the ager publicus in excess of 500 iugera and distributed the ager publicus to rural Roman citizens (apparently at the expense of the allies, though our sources are not the clearest on this point). Roman citizens--and the allies--could already occupy the ager publicus, however, meaning that the Gracchan land commission was not organizing the mass settlement of the ager publicus. Instead, the lex agraria established a board of three commissioners that would review holdings of the ager publicus to determine what holdings were above the 500 iugera limit imposed by a previous law and to survey the ager publicus more efficiently to distribute what was remaining to unlanded rural citizens. The Gracchan land bill neither took away private land nor did it massively populate unsettled land. Rather, it established clearer small landholdings and privatized (or at least established security on) the ager publicus, which legally could be occupied by anybody who paid the necessary tithe in kind to the state. In this it doesn't resemble the Homestead Act of 1862 very much at all, which established the mass settlement of previously uninhabited (at least by white settlers) land, exclusively for private use from the start. Moreover, the scale of Ti. lex agraria is an order of magnitude smaller. The ager publicus offered substantial land for small holdings (ten iugera? Thirty iugera? It's not clear how large the usual distribution was) but was hardly on the scale of the American frontier in 1862. The Gracchan agrarian bill specifically excluded the ager Campanus, the enormous expanse of highly fertile land around Capua, and the ager publicus distributed likely consisted only of fairly (disappointingly, even) small areas of land immediately around a couple of cities in southern Campania and possibly some land in Apulia and Lucania (following Roselarr).