"New Zealand is not collectively owned, it is privately owned," Dr Whyte said.
Act would also abolish the RMA, Dr Whyte said.
"The problem with the Resource Management Act is not in its administration, the problem is with the very conception of it."
The Act was "an assault on private property rights that stifles investment and economic growth", he said, blaming the Act's restrictions for the increasingly expensive property market.
Act instead would return a "sensible plan based on private property rights".
Other policies included removing all race-based policies, cutting the "absurd money-go-round" of government welfare, ending "crony capitalism", encouraging more charter schools and raising the retirement age to 67.
"Sometimes it's better to admit that you're wrong and break a silly promise," Dr Whyte said, in reference to Prime Minister John Key's long-standing promise to resign from the top job rather than increase the retirement age.
Dr Whyte said Act was the "only [party which] resists the temptation to buy votes with taxpayers' money".
He vowed to reduce "tax-funded goodies for people who are not hard up", such as Working for Families payments and interest-free student loans, branding them 'middle-class welfare'.
"The people who receive these benefits are the very people who pay for them. By cutting middle-class welfare we can reduce the personal taxes paid by the middle class from 33 per cent and 30 per cent to 24 per cent."
Urging people to vote for Act, he said: "National and Labour are no less disappointing than they were 20 years ago. Anyone who really believes in personal responsibility and individual liberty, anyone who believes the answer to every problem is not 'the Government should do something' still has only one party to vote for," he said.
"Act is still the only party that wants big individuals and small government."
During the launch, Dr Whyte also criticised other political parties, describing the possibility of a left-leaning coalition government as a "Frankenstein" monster.
While National was ahead in the polls, Dr Whyte said Labour and the minorities could still get enough votes to form a government.
"A Frankenstein Labour, Green, internet-Mana, New Zealand First government may be unthinkable, but it isn't impossible," he said, urging people to vote for his party.
Internet-Mana was "the crazy tangled mess of hair stitched onto the scalp" of Frankenstein's monster, he said with "lunatic" policies; the Greens were the face "grinning inanely below its swivel-eyes"; and Labour was the "big flabby torso".
"It's over to us again, the people of Epsom are doing their bit, David Seymour is door-knocking his way to victory in Epsom, now we need to get a number of Act list MPs into Parliament," he said.
Labour leader David Cunliffe said scrapping the OIO was a ridiculous policy "but at least now we know what National really wants to do".
The OIO was necessary "to make sure we don't sell out our children's birthright to foreign speculators", he said.
Greens co-leader Russel Norman said Act's proposal would "destroy the dream of ordinary New Zealanders who would like to be able to buy a farm in their own country". "They will simply be priced out of the market."
"Both the RMA and the OIO can serve as important protectors of our environment and our economy and removing them would be incredibly damaging for New Zealand, Dr Norman said.
"ACT's proposals show what another three years of an National-Act government would be - more foreign land sales and more environmental degradation."
Prime Minister John Key said he was not in favour of scrapping the OIO.
"Look, we toughened up the Overseas Investment Act in 2010. Our view, as you've seen this campaign, has been broadly set in about the right place.
"New Zealand needs capital to grow quickly, if we don't have that capital it has an impact on jobs, but we've got no appetite to loosen the Overseas Investment Act."
