The web browser you're using can do much more than just open websites. Google Chrome and its derivatives actually support a wide variety of media formats and office documents. Some of them are supported by default while others require some additional installations. Here are the files that you can open with your web browser.
Step 1: MP3 Music
You can play an MP3 music file with a Google Chrome web browser. All you need to do is right-click on an MP3 file in a folder on your PC and choose "Open in Google Chrome". This is perfect for opening a single music file.
However, if you intend on listening to full albums and creating playlists, Citrio Browser — a browser similar to Chrome — has this option.
The Media Player can be accessed via a pinned tab. Inside there's a fully functional media player where you can create playlists and listen to the music.
Step 2: MP4 Video
The previously mentioned Media Player in Citrio browser can also play video files. Fullscreen mode is available, just as shuffle for the video files playlist. Files can be opened via a context menu or by clicking on the folder icon inside teh player.
Step 3: PDF Files
Google Chrome can open PDF files by default. If you come across a PDF file online, Chrome will open it in a separate tab for viewing. Chrome and Citrio can be set as a default program for opening PDF files.
Step 4: PPT Presentations
You can open (but not edit) PPT presentations even without having Microsoft Office suite installed. For this you'll need an official Google Chrome plug-in called Docs PDF/PowerPoint Viewer (by Google). It's available for free in Google Chrome Web Store.
After installing the plug-in, you'll be presented with a list of file extensions that can be opened with the said plug-in. All of them will be opened using Google Drive and you don't need a Google account for this.
When you find a PPT file available online, right-click on the link and select Open with Docs PDF/PowerPoint Viewer.
Step 5: DOC Text Files
The same plug-in (Docs PDF/PowerPoint Viewer) works just fine with DOC files. They are also can be opened from the context menu while browsing.
Step 6: BONUS! Play Retro Games
Unfortunately, there's no way to use a browser as an emulator for old video games. There's no plug-in that allows you to open ROM-files. However, there's a site that works as an emulator and allows you to play a ton of classic console games. Head over to playretrogames.com and enjoy cool retro games (they support gamepads).