He said his party was standing on "a record of progress in government and vision of the future".
Mr Rennie said: "We are now closer to our ambition of creating opportunity for everyone. But with wins for the Liberal Democrat in this election we can make it a decade of opportunity."
He added that his party's offer was to create a "decade of opportunity for everyone in our country".
When questioned on whether people should vote tactically to keep the SNP out, he said: "In the 11 seats that we hold, it's very clear that if you want to stop the SNP, the Liberal Democrats are best-placed to do that.
"People will use their vote intelligently throughout the country and I would encourage them to do so."
He added: "We're prepared to work with the SNP in other areas, and we have done so in councils and we have done it in the Scottish Parliament.
"But it would be unreasonable to put them in charge of an institution that they are against.
"You could just imagine Alex Salmond, deputy prime minister, and as soon as you have turned your back he's got his screwdriver out trying to take the country apart.
"That's not who you need in charge of the UK and we have said that is not reasonable."
By Brian Taylor, BBC Scotland's political editor
It was, said Willie Rennie, a question of Kipling. No, nothing to do with cakes even although the location was a patisserie in South Queensferry.
The Kipling at issue was Rudyard of that ilk, story writer, poet and, for a spell, Rector at Scotland's oldest and finest university.
These are not particularly encouraging times for the Liberal Democrats. Polls suggest that they may be in trouble in Scotland and throughout the UK.
Despite that, Mr Rennie was unrelentingly upbeat as he launched his party's Scottish manifesto. Quoting Kipling, he said the Lib Dem attitude was "if you can keep your head when all about you are losing theirs".
Pedant that I am, I vaguely recollected that the verse continues "…and blaming it on you". The Lib Dems perhaps feel they have had more than their proportionate share of assigned blame of late.