Years ago, someone marketed a gadget that was designed to keep a bicycle from rolling while parked. It was a small clamp of sorts that attached to the downtube and could be pivoted down to grab the front tire and immobilize it. Does anyone know what this was called and if they can still be found?
Flickstand by Rhodegear. Not made anymore AFAIK. It didn't really keep the bike from rolling, but it did keep the front wheel pointed straight ahead and therefore made the bike more stable when leaned against something. I sometimes use a 'parking brake' instead. Just a rubber band that I keep arround a brake lever and use to hold the front brake on while the bike is parked. A velcro strap works well for this too.
Zoom zoom zoom zoom bonk
When touring I used a piece of velcro around the brake lever.