Hubspot has just announced a Series D round of funding for their marketing-as-a-service platform. Investors include some very big names like Google, Salesforce and Sequoia, which shows how much interest there is in its service aimed at small businesses. It's also a big boost for the Boston startup scene, as Hubspot is now one of the fastest growing SaaS companies in history by revenue, only behind Salesforce according to their CEO Dharmesh Shah.

Along with main competitors Eloqua and Marketo, Hubspot helps small businesses move away from traditional cold-calling and display advertising and into the new world of social media, search engines and blogging. On my recent visit to Boston, Shah explained to me that the initial idea came about when he noticed how much traffic he was able to drive through his OnStartups blog, when many of the businesses he was helping were struggling to get a fraction of the exposure.

To solve that problem, he set out to build a service that makes it simple for small business owners to use search ads, blogging and Twitter. The challenge has been creating tools that actually help small companies with little time or experience of the new technologies.

That's meant creating simple, actionable reports, as well as educating its users in the effective online marketing through initiatives like Hubspot TV. With 4,000 paying customers, its approach seems to be paying dividends.

Perhaps unsurprisingly considering that six out of its eight executives went to MIT, the bulk of the investment will be going into research and development to support "an ambitious product strategy that calls for building a complete and fully-integrated marketing platform". It does seem like it is a strong contender to become the equivalent of Salesforce for the marketing world, which will be a boon for small firms struggling to adapt to the online world.

Disclosure: HubSpot is also a sponsor of a forthcoming series on data science, which will appear on ReadWriteWeb later this month.