The market for sweetly named smart-phone assistants is heating up, as Siri, Apple’s iPhone-based virtual helper, just got a new “frenemy” named Evi.

Created by True Knowledge, a Cambridge, U.K.-based semantic technology startup, Evi, like Siri, can answer questions posed aloud in a conversational manner. But unlike Siri, which is only loaded on the latest iPhone, Evi is available as an app for the iPhone and phones running Google’s Android software.

Siri and other personal assistants are still fairly limited. As they become more popular, established companies and startups will need to expand the range of tasks they can perform. True Knowledge is hoping the semantic database it has built up over the past few years could provide this edge.

Evi’s availability and promise as an artificial intelligence app, coupled with its low price (99 cents on the iPhone and free on Android phones), caused its popularity to skyrocket following its Monday release, and made it difficult for those downloading it to try it out.  Evi isn’t the only Siri competitor—and in fact its capabilities are somewhat different from Siri’s offerings—but plenty of smart-phone users, it seems, are eager for Evi’s help in particular.

Evi uses a platform with hundreds of millions of data points that True Knowledge developed over several years (initially for Web search). Information in this database has been tagged to add meaning and context. For example, Apple is classified as a “company” and Tim Cook is classified as a “person” and a “CEO.” True Knowledge founder and CEO William Tunstall-Pedoe says this allows the app to understand all sorts of things—people, places, buildings, colors, and more—and how they interact, which helps the app find the right answer for a wide range of questions. In addition to all this information, Evi, like Siri, can access data on some outside websites.

Essentially, the app takes your spoken or typed question and uses its vast store of knowledge along with outside data from websites like Yelp to give pertinent answers. This is similar to how Siri works, but Apple’s assistant focuses more on accomplishing tasks, such as making calls, setting alerts, or dictating text messages, by working with the iPhone’s other apps. Evi does not do these things, but Tunstall-Pedoe says it will eventually be able to take on more tasks.

For example, asking Evi, “What’s a good recipe for chocolate mousse?” yields specific recipes. Ask Siri the same question, and you’ll receive a suggestion to search the Web. Similarly, if you ask Evi, “When is the next national holiday?” the app will respond with Monday, February 20, which is Presidents’ Day. Siri pulls a result from computational knowledge service Wolfram Alpha that doesn’t make much sense.

Evi also understands what you like and don’t like, if you’re willing to share. If you think one of Evi’s answers is particularly good or bad, you can let it know by giving a thumbs-up or thumbs-down.

And while Siri allows only voice input, you can ask questions aloud or type them to Evi (both respond aloud and with on-screen text). On the iPhone, Evi, like Siri, uses technology from Nuance Communications to power the speech-recognition function, so True Knowledge charges 99 cents to cover its licensing costs. The Android version uses Google’s own speech recognition capabilities, so that app is free.

Nova Spivack, founder of semantic Web service Twine and CEO of social-media aggregation service Bottlenose, expects a smart-phone maker to license Evi for inclusion on its own handsets.

“I’m sure they’re desperately hunting for a Siri killer,” he says.

Unfortunately, many would-be users haven’t been able to experience it themselves yet. Since its Monday release, Evi’s servers have been inundated with traffic as tens of thousands of people have downloaded the app and attempted to pose their own queries. The app is currently only available in the U.S. and U.K.

Trying to ask Evi a question throughout much of the week usually elicited a response such as, “I’m on it” or “I’m working on it,” followed by “I’m having trouble getting a response from my servers. You might want to try again in a minute.”

This has caused a backlash from frustrated users, who have given it negative reviews on Apple’s App Store and Google’s Android Market.

The team behind Evi is working on it, though. Tunstall-Pedoe says the company has already added “huge” amounts of server capacity to handle the app’s popularity, and continues to do so.

And he’s confident that, once people are able to use it, they will like it. “At the heart, she understands what you’re saying,” Tunstall-Pedoe says.