Vendors are scrambling to offer open-source application stacks as an alternative to integrated sets of proprietary applications that have long locked users into the technology of a single supplier.

Some vendors and analysts, however, are quick to criticise the emerging stacks, contending that they could lock in users the same way integrated stacks of a single vendor's applications have in the past.

Vendors hawking open-source application stacks whose integration is precertified include HP and IBM, Linux purveyors, Red Hat and Novell, and independent support providers such as SpikeSource, SourceLabs and many others.

"Stacks are rigid and deterministic," CEO of open-source software provider Simula Labs, Winston Damarillo, said. "They are prefab solutions, which most customers don't really want."

Simula Labs earlier this month announced its Community-oriented Real-Time Network (Core), which it described as a flexible framework for building, running and managing open-source software. Simula Labs also announced that open-source software providers Covalent Technologies, LogicBlaze, Megere, WebTide and Chariot Solutions had agreed to support Core.

The Core offering allowed users to customise open-source stacks, offering more flexibility than the precertified stacks, Damarillo said.

CIO at Home Insurance in New York, Davis Tharayil, is in the process of testing another alternative to a precertified open-source application stack: a custom server appliance from rPath that's designed to integrate Ingres' open-source database with a stripped-down version of Linux.

Home Insurance tested the appliance as part of its search for a lower-cost alternative to Oracle databases running on Solaris-based servers.

Tharayil said that the insurer did not consider emerging precertified open-source application stacks in its search for a plug-and-play product.

"A full stack just wasn't necessary," Tharayil said. "I've been in the business for 35 years. Every time something new comes along, they say it's a silver bullet. I still haven't found one."

An analyst at The 451 Group in New York, Dennis Callaghan, said the rPath model is impressive, though he noted that the company had a pretty small niche and customer base at this point.

An analyst at US consulting firm RedMonk, James Governor, said the tidiness of open-source stacks would likely continue to appeal to some customers despite their rigidity. He suggested that the true standards-based component modularity promised by service-oriented architectures would probably make the current stacks less relevant.

Application stacks have a long history among mostly large vendors of proprietary software, such as Microsoft, IBM and Oracle. Such vendors contend that their integrated software products can boost interoperability and cut costs, though suppliers of best-of-breed software often note that such products also lead to vendor lock-in.

To date, the task of integrating open-source software is mostly the responsibility of corporate users -- or their highly paid consultants. Such projects could easily wipe out the savings from using free software.