IBM said Thursday that it's acquiring Isogon Corp., a privately held maker of software that businesses use to track and manage applications running on their mainframe computers. Financial terms of the deal, expected to close in the third quarter, were not disclosed.

IBM will make Isogon's software products part of its Tivoli line of asset-management tools. The acquisition complements existing Tivoli products that help companies track their inventory and usage of applications running in distributed server environments.

A number of multinationals, including Nissan Motor Co. and Boise Cascade Co., use Isogon products. The company counts more than 200 customers worldwide. Research firm IDC estimates that spending on IT-asset-management tools will increase from $971 million in 2004 to $1.33 billion in 2009.

The Isogon purchase is the latest in a string of software acquisitions IBM has made in recent months. In May, the company closed its $1.1 billion acquisition of data-integration specialist Ascential Software. Also in May, it purchased Gluecode Software, a provider of subscription services that support open-source application servers such as Apache.

In a recent interview, IBM software chief Steve Mills said the company is looking to bolster the richness of its middleware offerings. "We're trying to get a very complete environment," Mills said, adding that more such acquisitions are a likely part of IBM's future. "Our acquisition pattern is going to follow the pattern of the past; we're in the middleware space."