Unless you're planning on allowing people other than your group of friends to watch the game, any group video chat or screen sharing software would be perfect for your needs.
Google Hangouts have incredibly low latency (< 1 second in my experience) and allow you to share your screen with others in the chat. Google Hangouts are also free if you already ...
To my knowledge, you can't explicitly start streaming.
What you can do is set your security settings so that the public can view your streams.
It appears to make the stream show up in the public section as I've had random people start my stream before when I was playing La Mulana.
Updated for 2020:
Now that Mixer is gone, the best option by far has been Discord. It has even lower latency than Mixer did, and it automatically works with Discord voice chat, so you don't need to do any complicated setup to avoid people hearing themselves on the stream!
Just for 2021 and onwards a new view on this topic:
While Twitch and Youtube (and Steam Broadcast) still focus on massive amount of viewers (obviously), latency still takes a hit with that services. Apparently there are ultra-low-latency modes in Youtube and Twitch (look up this link) and they are "fine" but it's still meant for streaming for a big ...
For what it's worth, my personal experience was that Hitbox has far less stream delay than Twitch, which was why I preferred it over the more popular site. Something closer to 5-7 seconds was the norm, from what I recall. I haven't personally tried Steam Broadcasting in any significant amount, so I'm not sure how it compares.
(Just in case, disclaimer: I ...