Salesforce.com has continued to tread the fine line between building an ecosystem of partners and scaring away one with the agreement to buy InStranet, a developer of knowledge base software for customer-support centres.

The $31.5m deal is Salesforce’s biggest acquisition and raises questions about the firm’s lofty ambition to build a partner hub as big as the one Microsoft built for Windows.

InStranet offers its wares on Salesforce’s AppExchange, a marketplace that the company likes to describe as an iTunes for applications. This is not the first time Salesforce has raided AppExchange to buy small participants but the tactic might send out bad signals for companies that want to compete for buyers’ attention on equal terms. Of course, many firms would love to be acquired for Salesforce if the price was right but for companies that want to compete in the long term, the sense that Salesforce could at any moment enter the market and compete there might alarm.

With Office, Microsoft pretty well closed down the market for Windows spreadsheets, word processors, presentation software and databases but by that point independent software vendors needed to sail on the Redmond mother ship. Salesforce is not as far advanced, however, and has to play a delicate game to win the loyalty and support of a legion of ISVs if it is to realise its big plan.