As of last year, there were roughly 1.5 million nonprofit organizations (NPOs) in the U.S., with about $1.6 trillion in aggregate revenues. Interestingly enough, about 83,000 NPOs reported $1 million or more in revenues.

What's more, a growing share of revenues is coming from online giving. The amount was nearly $7 billion last year. One of the firms that's capitalizing on the trend is Convio. And the company has recently filed to go public.

Convio develops on-demand software that helps NPOs with fund raising, advocacy, e-mail marketing, and web content management. There are about 1,200 clients, such as the American Red Cross, American Cancer Society, CARE, Public Broadcasting Service, Shriners Hospitals for Children, and the Smithsonian Institution.

What's more, early this year, Convio acquired GetActive, which has a platform for advocacy campaigns and content management. It also has been a boost for the customer base.

Last year, Convio generated $34.3 million in revenues. However, the net loss is a hefty -$12.5 million.

The lead underwriter on the IPO is Goldman Sachs (NYSE: GS) and the proposed ticker symbol is CNVO. You can find the prospectus on the SEC website.

To check out other IPOs, click here.

Tom Taulli is the author of various books, including The Complete M&A Handbook and The Edgar Online Guide to Decoding Financial Statements.