Want a snappy scrambler for stumptown I live in Portland, Oregon and I need a bike to ride to work. It's about five miles, with one steep but not long hill. I used to have a track bike with a freewheel that was really nice for Salem, which was a flat commute. Sadly stolen. I loved how fast it accelerated, it helped a bunch in traffic. Hills were killers on my knees, ouch.

Was thinking about maybe two or three gears. But as a cassette in back would make it less snappy off the line, I was imagining a front derailleur only. Is that implausible? Maybe having a chain tensioner at all would kill any snap. Do they make a Hammerschmidt for road bikes? Are there any frames designed for this?

Frame something closer to a racing geometry than a touring geometry, since I won't be taking many long rides, if any. 

Also, weight, like to keep it not much over 20lbs. So, not a hybrid frame. 

Disc brakes I am in love with from years of mountain biking, and would help control and maintain stopping power in this rainy climate; I don't know how heavy the road discs are however.

So.. a track bike with disc brakes and a front derailleur? Start with a cyclocross? Is there the perfect bike out there already made? Am I nuts? Any ideas?

Thanks!

Edit, to respond to comments:

What I mean by "snappy" - I found that using a super tight chain on a single back ring lets me apply speed faster than one where i have to take up slack first - i can make quicker adjustments to unaware cars. It's the same reason that I like disc brakes, more control. 

Sorry if my experiences and desires bother some of you, that wasn't my intent. I follow all the bike laws and ride politely. 

@mattnz Thanks for that suggestion, I will look at internal hubs again. A few years ago I looked at Rohloff's but I decided they weren't a good choice, mostly due to weight and ease of maintenance, but it appears that they have updated their lines quite a bit. I think SRAM has one too. Still be heavy I think which would add to angular momentum. There are also the Schlumpf Speed Drive planetary front cranksets.
With what you envision - A single cog in the rear and a triple crankset up front - you would still require a rear derailleur to take up the chain slack since the chainrings have such large difference in diameter. A chain tensioner would not cope with the slack created from shifting from a 42 to a 32 tooth chainring, for instance.

Since you'll need a rear derailleur for a multiple gear solution anyway, you might as well go with a cassette and single chainring.

For disc brakes you're limited to mechanical (like Avid BB7s, TRP Spyre) or the cable actuated hydraulic calipers (TRP HyRd) unless you spring for shimano Di2. 

The closest you'll get to a track/road frame that has the necessarry reinforcements and mounts for disc brakes is likely a cyclocross bike or some of the newer endurance road bikes (Trek Domane as an example).

You're unlikely to get something exactly as you envision, but with a few compromises (cyclocross with a cassette) you should be able to make things work.