Don't let your old Mac device collect dust. Image: iStock Unreleased/Getty ImagesShareYouve set up your new Mac and everything is great. The problem: Your old device is still sitting on your desk, waiting for you to decide what to do with it.Youve got options. You could factory reset your old Mac and sell itthey tend to hold at least some of their value. But it might be worth more to you in the house, assuming you can think of something to do with it. Recently we told you about uses for your old iPhone or iPad. Here, in the same spirit, are things you might be able to use your old Mac for.Smart TVs are great when they work but most of the time its easier to watch things in a browser. I constantly find myself fiddling with my smart TV to do something that would take five seconds on an actual computer with a browser. My solution: Connect an actual computer to your TV and use that. Your old Mac could be perfect for this, assuming its either a laptop or a Mac Mini. Youll likely just need an HDMI cable (you might need a Thunderbolt adapter if your Mac doesnt have an HDMI port). Get the Popular Science newsletter Breakthroughs, discoveries, and DIY tips sent every weekday. By signing up you agree to our Terms of Service and Privacy Policy.This setup is particularly nice if you get a wireless mouse and keyboardyou can control everything from the couch. And, as an added bonus, any Mac can be used as an Airplay receiver. This means you can share your iPhone or iPads screen and audio to your TV. This is very useful if your smart TV doesnt offer Airplay.Theres one Mac type that wont work well for this: the iMac. Plugging what is essentially a screen into another screen is going to be clumsy at best, but you could just use your entire old iMac as a streaming TV for a spare bedroom or any other space where you might want something on in the background.Retro GamingSuper Mario Bros. is always a good option. Screenshot: OpenEmu Weve talked about turning an old Wii into the ultimate retro gaming device, and that works pretty well. Do you know whats even easier? Setting up OpenEmu (the best emulation software out there) on a Mac. Theres also RetroArch, if you prefer. You can add ROMs from dozens of systems and then connect a controller to your Mac. After that you can just lean back and play. I think this works best if your Mac is hooked up to a TV, so it basically works as a game console.Home ServerScreenshot: Apple Whether you want to share a few files on your local network, which you can access your computer from an iPhone or iPad or set up a private email server, an old Mac can make for a pretty good server. This is particularly true of the Mac Mini, which you can easily set up in a cabinet or drawer. Just set up the Mac, open the System Settings and head to General > Sharing. From there you can turn on file sharing, media sharing, and more. You can even enable SSH access, if you know what that is (if you dont, dont worry about it). Basically you can turn your Mac into a viable home server pretty quickly.Time Machine BackupSpeaking of network shares: You can back up your new Mac to your old one using Time Machine. Its a great way to back up your new Mac without having to remember to plug in the backup drive regularly. Just create a shared folder specifically for the backup on your old Mac and point Time Machine to it. Ive tried a lot of alternative ways to run Time Machine back ups over the network, including a Raspberry Pi, but none worked as well as backing up to an actual Mac. If youre running on as a server anyway its worth considering.