It’s remarkable how Pinterest has been able to gain such traction in the social media space with such dominant forces like Facebook and Twitter to compete with, although rather than directly competing, Pinterest has managed to use Facebook and Twitter to its advantage. Users can create Pinterest accounts with a log-in from either, and Pinterest has certainly benefited from the “frictionless sharing” of Facebook’s platform.

Pinterest may be poised to grow significantly more thanks to a couple of recent moves. For one, they finally removed the need to receive an invitation to sign up. In other words, you no longer need to know someone that is already a user and wait to be invited by them, or request an invitation from Pinterest yourself and hope they give you one.

Secondly, this week, Pinterest finally launched mobile apps for Android, iPhone and iPad.

Pinterest said in a blog post, “iPad owners may have the best Pinterest experience yet. Our new iPad app is perfect for sitting on the couch, on a train, or in bed where users can effortlessly discover, save and organize the things that interest them. The app offers users new ways to engage with pins, whether swiping the screen to resume browsing after viewing a board, or using the embedded browser to see what others are pinning from their favorite sites.”

“iPhone owners have made it clear that they want to see more pins,” the company said. “The faster, redesigned iPhone app introduces a 2-column layout that lets users see more, so that they can find the pins they’re looking for and get back to their lives more quickly.”

“Android owners have been very vocal with their requests for an app – every product announcement we’ve recently made has resulted in the question ‘What about an Android app?’ We were listening, and our custom-designed Android app makes it simple and fast to pin, so that the time you spend on Pinterest is as productive as possible,” Pinterest said. “We also made sure the app works well on Android phones and tablets, regardless of your device’s cost, speed or screen size.”

The Android release includes the Kindle Fire, by the way.

Pinterest has covered the major smartphone and tablet devices on the market, and for users of other devices, Pinterest’s mobile site still works just fine. Now that they’ve shown that they really do care about mobile users, it seems likely that they’ll launch on other mobile platforms, such as Windows.

Pinterest’s growth and cross-platform compatibility could be just what the doctor ordered for e-commerce businesses looking to get more web traffic from social media, especially now that they have to pay Google to be listed in Google Shopping. There are various products coming out designed to get Pinterest users interested in, well, products.

Take ShopInterest, for example, a DIY online shop for merchants to create pinboards of the stuff they sell.

Other e-commerce products are simply using Pinterest as inspiration. Just this week, for example, ShopVibe “emerged from stealth-mode” to announce its new social shopping platform that enables people to keep track of their shopping, describing it as “Pinterest meets Shopping.com”.

In general, brands themselves are flocking to Pinterest. According to a recent study from SimplyMeasured, 51% of the top 100 global brands now have Pinterest accounts.

Pinterest’s increased presence on mobile could sway brands to get more involved, as much as it could sway users. Either way, the brands will follow the users.

Pinterest has also been expanding its category offerings. The more it does this, the more valuable the site could be to online merchants.