Tamron has announced it is developing the company's first foray into a zoom lens for Micro Four Thirds, the 14-150mm f/3.5-5.8 Di III VC. That's the full frame equivalent of 28-300mm, with 17 lens elements in 13 groups. It'll feature Tamron's VC (Vibration Compensation) optical stabilization system (which Panasonic shooters will doubtless be thankful for), and a stepping motor for super-quiet focusing.
Since this is an announcement of development, there's no indication of when the lens will be available, but we do know that it'll have a metal lens barrel, and be available in black or silver.
The Tamron lens will weigh just 9.9oz, and clock in at 3.2 inches, with a 52mm filter size. By comparison, that has a slightly wider maximum aperture than the Olympus 14-150mm f/4-5.6, but is nearly identical in size. It's also substantially smaller and lighter than the Panasonic 14-140mm f/4-5.8, and again a bit brighter.