Unfortunately this won't be for everyone, as EA has said that only a, "few thousand," will be given access to this Alpha, but those few thousand will be the first few Mac gamers to have a go with Origin on their favourite OS.
No word on how you guarantee your position as one of the Alpha participants, but the best bet is to at least make sure you have the client downloaded - do so here - and keep your fingers crossed.
You won't be able to buy any games with this alpha release, since the store tab won't be live, but it will be once the full version is launched later on this year. Twitch streaming won't be available either, but EA has promised it will be activated, "as soon as possible."
If you don't have any games on Origin already, you won't be out of luck completely, as EA are including a free version of its PopCap's BookWorm, you know that game that's six year old. Generous right?