A really old Apple computer can fetch a fortune at an auction these days, but more recent models that you can easily pick up on eBay aren't going to make you a great deal of money -- especially if they no longer work. But instead of sticking them in your garage and leaving them to collect dust, why not turn them into something useful?

In this gallery, we'll show you 11 old Macs that have been given a new lease of life, like the Mac Pro that's now an aquarium, a group of Macintoshes turned into planters, and an old iMac G4 that's been transformed into a desk lamp.

Photo: theappleguru, eBay

This old Mac Pro G5 case has been transformed into a gorgeous aquarium that would look right at home in any Apple fan's living room. It's fully functional, and complete with lights and an air pump.

"In keeping to my fascination with reusing and recycling things to fulfill a new design and function, this fish tank built from a Apple G5 desktop seemed like an ideal way to give a new life to a dead machine," says creator Michael Garito.

Garito used acrylic to make the tank that lives inside the case, and its miniature air pump is concealed beneath it where the Mac Pro's power supply would have lived.

Garito is currently selling this particular tank, and you can contact him via his website below if you're interested.

Photo: Michael Garito, mgarito.com.

Another Michael Garito creation, this aquarium was made out of two old Apple monitors sandwiched together. Due to its strange shape, Garito had to build a custom filtration system for this tank.

"I built a filtration system that is submerged in the tank, hidden behind the central 'hide'," he explains. "I did not want the aesthetic of the tank diminished by air tubes running over the side so they, along with the filter's power cord, and the tank's drainage tube are all discreetly ran out of the bottom and through the monitor stand."

This tank seems a little trickier to build than the Mac Pro tank, but it looks pretty spectacular. Garito donated this one to an elementary school.

Photo: Michael Garito, mgarito.com

If you've got an old iMac G4 knocking around, turning it into a stunning desk lamp is actually easier than it looks. This particular model was sold on Etsy, but there are lots of guides to making your own.

Photo: SewWhatSherlock, Etsy

Perhaps the greatest way to breath new life into an old Mac is to turn it into a "Hackintosh." That's doing away with its old components, using its case to house a brand new PC, and then installing OS X on it.

Of course, Mac Pro cases won't just take any motherboard and components, so you'll have to make a few adjustments to make them fit. This particular Hack Pro was put together by "Commander Zero" over on the InsanelyMac forums who details each modification that was made in the thread below.

Photo: CommanderZero, InsanelyMac

If you're not up to building a Hackintosh, how about gutting that old Mac Pro case and using it as a cable tidy instead. No one likes the sight of messy cables, but this "Power Tower" from Kiwidee looks great when it's all closed up.

Tucked away inside it there's an integrated power surge, three AC circuits, and up to 30 plug sockets. There's even a handy socket on the front of the case.

Photo: Kiwidee

These Macintosh planters are the ideal garden accessory for any tech freak who likes getting their fingers green - and they couldn't be simpler to make. Simply gut your Macintosh, cut a hole in its top, and fill it with soil.

Photo: Superchou, Flickr

Another simple hack, this one turns an old Mac Pro G4 case into a mailbox. All you need to do is gut your machine, cut a hole out of its front for your mail and install a door, then add some numbers.

Don't forget to make the case waterproof, though, because you could come home to soaking wet post after a rainy day.

Photo: Digitaldust, Flickr

When it's sunny outside, you don't want to be stuck in with your Mac. So how about turning it into a barbecue grill and taking it outside for some cooking. You can make your own by following the steps in this Imgur gallery. Photo: 100uf, Reddit

If you've got more than one Mac Pro case collecting dust, sticking a block of wood between them creates a beautiful bench like this one from Klaus Geiger.

Photo: Klaus Geiger

Another Klaus Geiger hack turns a couple of old Mac Pro cases into a set of drawers that even Jony Ive would be proud of. This one's a little harder to put together than the bench, but it's well worth the effort.

Photo: Klaus Geiger

This old Power Mac G4 Cube case makes for the fanciest tissue box you'll ever see. Creating this hack is as easy as swapping out the computer's old logic board, hard drives, and other components for a box of tissues. You can find step-by-step instructions via the link below.

Photo: Macgeek, Instructables

Purple Mac Pro Hackintosh

Unlike Apple's newest Mac Pro, which looks like a trashcan, this replica 2013 Mac Pro is made out of an actual trash can. It even comes with a matching toilet brush.

Purple Mac Pro Hackintosh, back view

Made by hacker JuanLobo, the replica is quite capable, boasting outputs for HDMI (three), USB, Ethernet, DVI and digital audio.

Purple Mac Pro Hackintosh, the guts

It was hard work getting all the components to fit inside the trashcan. The fan cooling the graphics card had to removed and flipped over. Another challenge was squeezing in the special power supply.

Purple Mac Pro Hackintosh, custom 3D base

To make everything fit, JuanLobo created a 3D model of Mac Pro's base. "It provided another 30mm of space that was desperately needed," he wrote on the project description.

The actual trashcan

This is the $53 Lunar Waste Bin used to build the replica Mac Pro.

Water-cooled PowerMac G5

This is a water-cooled PowerMac G5. "I've always loved the style of the PowerMac G5 enclosure," wrote it's creator, MrAhlefeld.

The original PowerMac G5 case

"I've sourced a PowerMac G5 from a local MAC shop in my city," said MrAhlefeld. "It was dirt cheap, cause one of the handles on the to was bend out of shape."

PowerMac G5, filling the coolant

"I will be using some of my old parts as I love my Eheim 1048 pump, just can't beat it at those noise levels," explained MrAhlefeld.

PowerMac G5, the cooling system

The coolant loop includes three beefy fans to dissipate heat. The original G5 ran so hot it had nine fans.

The HackinBeast tower

In September 2012, the HackinBeast was one of the fastest Macs on the planet with a whopping GeekBench score of 36,918.

The HackinBeast

Based on a pair of Intel Xeon X5690 CPUs, the machine’s total cost was $4,500. That’s less than half of an equivalent 2012 Mac Pro, which would have cost more than $10,000 and topped out with a Geeekbench score of 25,000.

Cooling the HackinBeast

Here's the beast's crazy cooling system. It's loaded with LIQ-702 Liquid Coolant (UV Green).

hackinbeasttower_logo

The HackinBeast's logo. “It took me from January 2012 to Sept 2012 (a total of 9 months); the same amount of time it takes to have a child,” wrote its maker, PunkNugget.

Mini G5

This is a mini G5, approximately half the size of the original. It was hacked down to size by prolific hacker neilhart. "This has been four months of 'fun' and I end up with a high performance machine that runs with the best," he wrote.

Hackintosh mini server

This Mac mini case has been updated with up-to-date components.

G4 Stormtrooper

With a Star Wars aesthetic, the G4 Stormtrooper Haswell has been updated with a speedy 17 processor. Painting the case was a lot of work. "I sanded all the parts, applied a coat of primer, sanded down, applied a second coat, painted it in black and white (two layers), sanded with steel wool, and finally applied three layers of varnish," said its creator, antonvodenitcharov.

G4 Stormtrooper, open

The G4 Stormtrooper is made for audio work. " I decided to built my dream Hackintosh," said antonvodenitcharov.

iMac G4 Hackintosh

Another iconic Mac, the iMac G4, gets an update from an Intel NUC mini-PC. "The project turned out great, and works terrific in early testing," wrote its creator, ersterhernd.

Water-Cooled Cube

This is the world's first water-cooled Cube.

The Cube's tiny cooling loop

This is the cooling loop for the water-cooled Cube.

Powermac G4 Hackintosh_

"I got excited by the idea that i could have a crazy powerful machine in ANY case I wanted," wrote modder rayd. "So naturally I picked the best looking case ever to be made; the Powermac G4 MDD." The Powermac G4 MDD runs OS X 10.9 Mavericks. Not too shabby!

Brix Pro Hackintosh

"Extremely small form factor micro PC kits are gaining steam," writes Tony of TonyMacX86. "Since the Intel NUC (Next Unit of Computing) was launched, many users have started using them as HTPCs, and even full desktop replacements."

Brix Pro Hackintosh Mini PC

Tony built his tiny Hackintosh from a Gigabyte Brix Pro mini-PC.

Hackintosh in an Xbox

There's no accounting for some people's taste. This modified Xbox 360 is based on a low-power Celeron processor. It's no speed demon, but serves well as a Mac-based media PC. "The idea was to make a small, cheap but yet capable machine, mainly intended for usage under a TV set," said its creator dj_aris.