Sometimes, the simplest ideas are the most effective. Read on to discover 11 creations, ranging from the ingenious to the downright silly, that remarkably turned out to be million-dollar ideas...

All dollar amounts in US dollars.

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 per pixel (around $1.60/£1.30 today). 

What was originally supposed to give the business student a way to fund his path through university ended up becoming a lot more...

The site's million pixels were arranged in a 1,000 x 1,000-pixel grid. 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 earned over $1 million (£800k) by 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, it'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 (around $1.44/£1.16 today), the app went on to make $10,000 (£8k) per day in its first year, and eventually over $1 million (£800k).

It was even downloaded by George Clooney, who admitted that he personally found 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.

Back in the 1980s and 1990s, 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 (£6.4m) a year in the early 1990s.

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 parts of the body. 

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 partner Abe Bookman took over, initially 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 (£8m) annually. In 2011, TIME magazine named the Magic 8 Ball one of the greatest toys of all time.

Yes, you read that right. 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, which retailed for $3.95 (around $20/£16 in today's money), caught the public’s imagination and, depending on who you ask, Dahl earned up to $15 million (£12m) during the mid-1970s.

Sadly, the craze only lasted around six months, with the rocks selling particularly well over Christmas. Due to falling sales they were discounted in 1976, just one year after they came out. However, Dahl lived comfortably and used his millions to open a bar. 

The Hula Hoop was invented by Richard Knerr and childhood friend Arthur 'Spud' Melin, who also developed the Frisbee. It ended up selling 100 million units when it was first released in 1958, and became popular among children and adults.

Despite Knerr and Melin being the ones to trademark the Hula Hoop, it's actually been around for thousands of years. It's 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.

However, it was only after the pair came up with the trademarked name and sold it via their toy company Wham-O that the invention became popular everywhere.

The Hula Hoop brought in $25 million in the first four months of its release, over $270 million (£217m) in today's money, and despite going in and out of fashion throughout the years, it remains one of the simplest inventions to earn millions. Today, the toy continues to sell in its millions worldwide and is estimated to generate over $200 million (£160m) annually.

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...

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 (£400m) in gross revenues since its launch.

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 (£400m) in gross revenues since its launch.

Velcro is now so common that it's hard to imagine a time before it existed. But back in 1941, George de Mestral noticed burs on his dog after a walk in the mountains and wondered if it could be used for something useful.

Mestral spent the next eight years researching how to synthetically recreate a bur. He finally produced a prototype and named it Velcro, a combination of the words 'velvet' and 'crochet'. It was patented in 1955.

After years of additional research and several redevelopments, NASA began using it for astronaut equipment. A few years later, shoe companies such as Puma picked up on the invention, finding it worked well for children's shoes. Today, it's used all over the world.

The company the invention gave its name to now generates revenue in the region of $1 billion (£800m) a year.

Despite not winning any fashion contests, annual sales of Crocs have regularly exceeded $1 billion (£800m) a year. Launched in 2002 by three friends, Crocs were made from a trademarked material which was marketed as “comfortable, lightweight, non-marking and odour resistant”.  

Initially marketed as a boat shoe, Crocs quickly became popular with medical staff and restaurant workers, people who spend a lot of time on their feet. Crocs made a comeback in 2017, and millions of pairs have been sold to date. While the aesthetic of these shoes is highly contentious, Crocs are certainly one of the most popular shoes of the past two decades and have even broken into the world of haute couture through high-profile celebrity partnerships.

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...

Nowadays, certain Beanie Babies can go for absurd amounts of money. The blue elephant Beanie Baby, for example, has sold for over $1,200 (£960) and the Princess Diana Beanie Baby for as much as $31,800 (£25.5k).

For these prices, it's not surprising that the simple but brilliantly marketed creation helped Warner create an empire that reportedly generated more than $1 billion (£800m) in annual revenue at its peak.

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

While it's unclear who the original inventor of the fidget spinner was, it led to a boom for the toy industry. Some estimates suggest the simple gadget has generated over $5 billion (£4bn) in sales since its release.

Now discover what tickets for history's most iconic gigs would cost in today's money

Updated by Alice Cattle