According to reports online today, and a release, Union Square Ventures, the venture firm that funded such names as Del.icio.us, FeedBurner, Etsy and Twitter, is investing $1.5 million in open source cloud computing service 10gen. 10gen's software stack is roughly comparable to Google App Engine "in that it provides a new stack of tools (database, grid management, application server) that are purpose-built to run in a cloud environment," according to the company. An alpha version of the company's platform SDK is available now as a free download.