Sometimes people make it look so easy to make a fortune you’re left wondering why we aren’t all millionaires. Here’s a list of inventions that range from the ingenious to the downright silly, but remarkably turned out to be million-dollar ideas...

At the age of just 21, Alex Tew made a fortune from the shockingly simple idea of selling space online. In 2005 he set up a web page where companies could buy space to advertise their wares at a cost of $1 (68p) per pixel. What was originally supposed to give the business student a way to fund his way through university without debt, ended up becoming a lot more...

The site's million pixels were arranged in a 1000 x 1000 pixel grid, and buyers could supply a tiny display picture, a URL and a slogan to pop up when the cursor hovered over the image. His simple plan worked when the page went viral, and Tew ended up earning over $1 million (£785k) through selling the advertising space to all sorts of different companies and organisations.

Entrepreneur Joel Comm has made millions from inventing the iFart app. Yes, you guessed right, that's an app that makes fart noises. The digital whoopee cushion was developed in 2008, when phone apps were relatively new. The app includes options to purchase different types of 'fart noises', such as 'burrito Maximo' and 'Howard the duck'.

Originally selling for 99 cents (78p), the app went on to make $10,000 (£8k) per day in its first year, and eventually over $1 million (£785k). It was even downloaded by George Clooney, who admits that he personally finds fart jokes "hilarious". Still available, but for the higher price of $1.99 or £1.99, It is now one of the top 100 most downloaded apps on Apple's App Store.

Inventor Albert Carter was inspired by a device used by his mother, who considered herself a clairvoyant. Carter's aim was to make something that would answer people's questions without any psychic ability. After years of developing various prototypes, the Magic 8 ball was born.

After Carter's death in the mid-1940s, his brother-in-law and business parter Abe Bookman took over, originally marketing the ball as a paperweight. However, after seeing its popularity with children, it began to be advertised as a toy. The device is now so popular that it’s still mass produced for children around the world, and sells in its millions every year, making an estimated $10 million (£7.8m). Back in 2011, TIME magazine named the Magic 8 ball as one of the all time greatest toys.

Paul Brown, the owner of a small precision-moulding shop, spent his days coming up with and rethinking the design of the bottle. He said: "I would pretend I was silicone and, if I was injected into a mould, what I would do." His work paid off in 1991, when he came up with the idea for a bottle that would open when squeezed but remain closed if no pressure was applied. The days of scraping ketchup out of a glass bottle with a knife had ended.

Brown’s invention was so popular that he earned over $14 million (£10.9m) from selling the design to many different organisations, but predominantly Heinz and shampoo companies.

Yes, you read that right. Literally a rock in a box of hay, complete with breathing holes, this simple toy was invented by former advertising exec Gary Dahl in 1975, who marketed the rock as a pet that requires absolutely no caring for. Dahl came up with this unique idea when listening to his friends complain about having to look after their actual real-life pets.

The light-hearted novelty gift caught the public’s imagination and, depending on who you ask, Dahl earned up to $15 million (£11.7m) during the mid 70s, despite them only costing $3.95 (£3.10) each. Sadly, the craze only lasted around six months, with the rocks selling particularly well over Christmas. Because of falling sales they were discounted in 1976, just one short year after they came out, but Dahl lived in comfort, using his millions to open a bar.

Back in the 80s and 90s, children were enthusiastically wrapping Snap Wraps around their wrists left, right and centre. Invented by teacher Stuart Anders, the bracelets reportedly brought in as much as $8 million (£5.5m) a year in the early 90s.

The overwhelming simplicity of Anders' invention pleased kids and pre-teens everywhere. The bracelet worked by simply slapping a straight piece of steel covered in colourful fabric to the wrist, which it instantly clasped itself around. Despite the popularity, snap bracelets were banned in several schools because of injuries caused by slapping the metal bracelets on the body.

The Hula Hoop was invented by Richard Knerr and childhood friend Arthur "Spud" Melin, the men also behind the Frisbee. It ended up selling 100 million units when it was first invented in 1958, and became popular among children and adults. Despite Knerr and Melin being the ones to trademark the Hula Hoop, it has actually been around for thousands of years. It is said that the Ancient Greeks used them as a form of exercise to tone their bodies and children have been playing with hoops for generations.

It was only after the men came up with the trademarked name, however, and it was sold by their toy company Wham-O, that the invention became popular everywhere. The Hula Hoop sold $25 million in the first four months of its release, and despite going in and out of fashion throughout the years, it remains one of the simplest inventions to earn millions.

Launched in 2008, the Snuggie concept wasn't original. In fact the wearable blanket was inspired by its rival the Slanket, which was the brainchild of Gary Clegg, who came up with the idea of a blanket with sleeves after he found he didn't want to take his hand out of his blanket to change the TV channel. But the rivalry doesn't stop there as it turns out both products actually came after the Freedom Blanket, a very similar concept...

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It may not have been first, but the Snuggie definitely won the wearable blanket wars. The cosy but practical cover-up has generated as much as $500 million (£392m) in gross revenues since its launch.

Velcro is now so common that it's hard to imagine a time before it. But back in 1941, George de Mastral noticed burs on his dog after a walk in the mountains, and wondered if it could be used for something useful. Mastral spent the next eight years doing research and trying to find out how to synthetically recreate a bur. He finally produced a prototype and named it velcro, a combination of the works 'velvet' and 'crochet'. It was patented in 1955.

After years of additional research and several redevelopments, NASA picked up the brand and began using it for astronaut equipment. A few years later, shoe companies such as Puma picked up on the brand and found it worked well for kids' shoes. It became a worldwide success, bringing in $100 million (£78.6m) revenue every year.

Originally invented as a therapeutic tool for kids with ADHD and autism, this simple spinning toy has sold to kids and adults alike since 2017. The spinners are designed to spin easily, without much effort, while being held in the centre. While many schools have banned the toy, amid claims that they distracted children from their schoolwork, many people have found them to act an effective stress reliever.

Despite it being somewhat unclear as to who the original inventor of the fidget spinner is, it led to a boom for the toy industry and they are now a $5 billion (£3.9bn) trend, despite similar toys being around since the 1990s.

Ty Warner's Beanie Babies have proved a collector's cult hit since the early 1990s. So much so that some individuals are willing to spend thousands of dollars for some of the rarer bears...

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Nowadays, certain Beanie Babies can go for absurd amounts of money. The blue elephant Beanie Baby for example has sold for over $1,200 (£1k) and the Princess Diana Beanie Baby for as much as $31,800 (£25k). For these prices, it's not surprising that the simple, but brilliantly-marketed creation has helped Warner create an empire reportedly worth billions of dollars.

Despite not winning any fashion contests, annual sales of Crocs have regularly exceeded $1 billion (£787m) a year. Launched in the early 2002 by three friends, Crocs were advertised to be made from a trademarked material which was “comfortable, lightweight, non-marking and odour resistant”.

Initially marketed as a boat shoe, Crocs quickly became popular with medical staff, such as nurses, and restaurant workers because of how comfortable they are for people who work on their feet. Crocs made a comeback in 2017 and have sold millions of pairs to date. While the aesthetic of these shoes are highly debatable, crocs are certainly one of the most popular shoes of the past two decades. 

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