Which Foreign Startups Are Doing Well In Japan "Under The Radar"?

2011-02-15 By Serkan Toto Japan Service Trend USA #bump #Evernote #hootsuite #Instagram #Seesmic #Tumblr

It’s no secret that in recent years, quite a few foreign (mostly American) web brands have made it big in Japan: Google, YouTube, Twitter, Wikipedia, Amazon etc.
But what about startups that don’t have huge budgets to internationalize, no staff in Japan and - in some cases - not even a Japanese user interface (usually a dealbreaker for most local web users).
Here’s a recent (yet surely incomplete) list:

Instagram (we just recently reported about the silly printed how-to-use-Instagram book available in Japan)
Foursquare (KDDI wants to help Foursquare to become bigger in this country)
Bump
Hootsuite
Jimdo
Tweetdeck
Tumblr (official data submitted from Tumblr to Quantcast shows Japan is their No. 5 market worldwide)
Seesmic

In 2010, Evernote established an office in Japan, the company’s No. 2 market worldwide, so it can’t really be part of this list - even though the app was already very popular before that.
Which foreign web and mobile startups flying under the radar in Japan have we forgotten?