Try Elementary OS, its based off ubuntu and is almost a dead ringer for OSX. It has the window management you are looking for as well as a couple of apps. Try Synapse as a replacement for Alfred.
The recent kerfluffle in which the ElementaryOS team changed their download page to try to hide the "free" option and said "We want users to understand that they're pretty much cheating the system when they choose not to pay for software" makes me super hesitant to even try it. I'm not sure I want to be using a Linux distro produced by people who think that free-as-in-beer is a bug.
Software has to be monetized somehow. SUSE and RHEL and Oracle Linux are monetized by subscriptions to support contracts. Slackware is monetized by sales of double-sided DVDs. Ubuntu is monetized by a mix of support contracts and begging for donations on the download page. OpenBSD is monetized by a a mix of donations and merchandise sales (including install CD packs and t-shirts and such). I'm not one to believe that ElementaryOS is any more or less sinful than any of those examples.