A California startup company, Vysr, is trying to improve on the web browser with a free add-on tool that lets you access services from sites without having to actually visit them.

The add-on, called RoamAbout, is available for Internet Explorer and Firefox. Once downloaded, it appears as a collapsible toolbar at the bottom right corner of the screen, with icons for services such as YouTube, Wikipedia, Map Quest and Flickr.

When browsing the web, users can find out more about a particular term by highlightin it and clicking on the Wikipedia icon, a box will pop up with a snapshot of the Wikipedia page about that item.

RoamAbout reflects the idea that users can take their favourite services with them as they roam about the web It was introduced by startup Vysr(pronounced "visor") in late March and has been downloaded about 10,000 times, according to CEO Guda Venkatesh.

Vysr has now opened its platform to let third parties develop further toolbar applications, which they can then try to make money from through advertising or other means. Vysr also added some new applications, including one for searching EBay, a music service from Grooveshark, and a comparative shopping service from one of its first developer partners, Viddu.

Viddu CEO Kiran Patchigolla said he was drawn to Vysr because it provides an unobtrusive way for people to use other services without having to open new browser tabs. He said it It took him a weekend to create a new view for his existing shopping tool so that it can appear in RoamAbout.

The applications available in Vysr today are still fairly limited, however - there are about a dozen - and Gmail and Facebook are currently the only ways to connect with friends.

That's why opening the platform to developers is important, but getting them on board without having a large base of users could be tough, said Barry Parr, a media analyst with Jupiter Research.

"To make this a success you need to have several million active users. With less than that, it's difficult to have much going on in the market, as an advertising platform or one that developers will be interested in working for," he said.

Vysr also has plenty of competition from other platforms vying for developers' attention, such as Facebook, and from other browser add-ons, including the many available for Firefox. Most add-ons are free, open-source tools, and not many have been successful as commercial businesses, Parr said.

In fact, history is littered with companies that have tried to build a business by extending or reinventing the ubiquitous browser. One factor in Vysr's favor is that more websites these days are exposing service interfaces for use by other sites, Parr said.

Venkatesh said other tools failed because they tried to change people's behaviour too dramatically. "The only paradigm change here is the idea of selecting something on a page and then invoking it in another service. Even then, I'm a bit worried. It's still a paradigm shift, but it's small enough that we believe it will work," he said.

Vysr also says it has something unique to offer. Part of the platform available to developers is a voice-over-IP service for adding calling capabilities to applications. Vysr claimed to be the only platform that combines the context of a web page with the social, sharing aspect and a communications platform.

"The implementation is nice, but it's too early to say if it will be attractive to consumers," Jupiter Research's Parr said.