User acquisition without investment

Everyone knows, that acquisition of clients for a web-service sometimes costs a lot, especially when you try to promote your product at highly competitive market. The question is, whether it’s possible to make you service sell without painful spendings on advertising and promotion?
My team developed and launched the tool of project management called askcow, which leaves far behind the most popular service for online collaboration -Basecamp, Wrike, JIRA and so on.
Is it possible to promote and make people informed about askcow without investments into PR, or we have to turn to fundraising in order to compete with 37Signals of Atlassian?