this is done as terrans, and there are quite a few variations of this, my fav one is the proxy 6 rax, as this is the fastest way of doing it and it purely relies on killing vills before your opponent can get anything.
this strat is done by Terran, either against Zerg or Protoss, never do this against another terran! i would rather do this to protoss than to zerg btw.
Buildorder:
- You start with 6 SCV's (vills), put all of them to a mineral field, they'll autofind their own mineral patch
- take one of them and go to the middle of the map, preferably a place your opponent won't scout very early.
- When you got 150 minerals, build a barracks
- When 75 minerals, get your Refinery up, when finished, put 2 SCV's in it
- As soon as the rax finishes, get a tech lab (costs 50/25)
- now build scv (8 pop) and wait till the tech lab is finished
- as soon as the tech lab is finished you should be able to build a reaper costs 50/50)
- cue another vill you should be at 10 pop, when reaper finsihed build another one, now you're popped ad build a supply depot with your SCV
- now take this reaper and go harass, snipe vills and go back and forth, reapers are fast and can jump cliffs up and down.
- remember the SCV which built the proxy rax? if you were good you could go to a mineral patch in the middle of the map while he was idle and grab 5 minerals, now put him forward and build a bunker with him right at enemy base in which you can garrison your reapers, they are protected in their and can still shoot :-P if your opponent attacks your bunker, repar it with your scv.
- now the thing with protoss is that they're building zealots 90% of the time which can be easily sniped off with hit&run, be careful with the cybernetic core, once that is built they can get their stalkers which own your reapers. i wouldn't suggest building more than 4 reapers, 2-4 is fine.
- snipe off vills whenever you can and get the pylon down which supports his buildings, they have low hp and if they're down and no other pylon is near, his buildings cannot be used

the replay is from 2 weeks ago or so but nothing from the latest patches has changed really so it can still be done.
in the meantime, get your eco going, build supply depots (houses) when necessary, get the orbital command upgrade at your command center (tc) and call down M.U.L.E.'s an build scv's. get a 2nd refinery at 17/18 and a 2nd rax too. now it's time to either tech to some useful unit like banshees or just go MM. from here on it varies but most of the time especially against newbies it's gg right here
be aware if he builds a forge cuz then he 's trying to get photon cannons in teh last patch the build time got increased so it should be harder for him to do so.
i only recommend this against zerg when he goes for fastexpand and generally more ecoheavy, otherwise this is predestined to bring the plans of your protoss opponent out of whack
in the attachment you will find a recording of me played weeks ago, the strat is still unchanged so it's all good.
the game was actually terribly played by me, and alot of stuff was not done(early scouting sucked, as well as keeping my eco going while harrassing,etc.), but it still shows a basic idea
if you don't like this no eco rush then go for the slower, but eco-heavier version of this. which would be
8 Rax Proxy Reaper:
SCVS 1-5 Minerals
SCV 6 Scout -> Proxy
7 SCV
8 SCV
8 Rax
8 Gas
9 SCV
9 Tech Lab
10 Reaper
10 Orbital Command
11 Reaper
11 Supply
12 SCV
by all means try this out it's alot of fun, especially with the bunker and garrisoning/ungarrisoning. :-P