CompactGUI is a standalone user interface that makes the Windows 10 compact.exe function easier to use.
What is the Windows 10 compact.exe function? It's a commandlet with a collection of new algorithms introduced in Windows 10 that allow you to transparently compress games, programs and other folders with virtually no performance loss.
Transparently? What does that mean? Transparent compression means that files can still be used normally on the computer as if nothing had happened - they don't get repackaged like Zip and Rar files do.
How is this different from the built-in compression in older versions of Windows? This is similar to the NTFS-LZNT1 compression built-in to Windows (Right click > Properties > Compress to save space) however the newer algorithms introduced in Windows 10 are far superior, resulting in greater compression ratios with almost no performance impact.Those with older HDDs may even see a decent performance gain in the form of reduced loading times as the smaller files means it takes less time to read programs and games into RAM.More information can be found here
Installation 
Download from GitHub Releases
Or:
Install with Chocolatey from Powershell or CMD:
choco install compactguiUses
Use this tool to:
- Reduce the size of games (e.g. Fortnite: 18.8GB > 10.2GB)
- Reduce the size of programs (e.g. Adobe Photoshop: 1.71GB > 886MB)
- Compress any other folder on your computer
Extra Features
- Visual feedback on compression progress and statistics
- Configurable list of poorly-compressed filetypes that can be skipped.
- Online integration with community-sourced database to get compression estimates and analyses
- Integration into Windows Explorer context menus for easier use.
- Drag-and-drop functionality
- Analyze the status of existing folders
- Shutdown/restart/sleep on completion.
See the Wiki for a list of 
and 
that have been tested
Important Note: Due to a bug in Windows, many of the Wiki results for larger games are inaccurate. Please consider submitting new results from within CompactGUI 2.5.0+ to rebuild the database of results
Screenshots
Background
Windows 10 includes a little-known but very useful tool called Compact.exe that allows one to compress folders and files on disk, decompressing them at runtime. With any modern CPU, this added load is hardly noticed, and the space savings are of most use on those with smaller SSDs.
As program folders and games can be shrunk by up to 60%, this has the added bonus of potentially reducing load times - especially on slower HDDs.
More information on the inbuilt Windows function can be found here and here or by typing compact /q into the commandline
This tool is intentionally designed to only compress folders and files. Whole drives and entire Windows installations cannot be modified from within CompactGUI - users seeking that functionality should use compact /compactOS from the commandline.
The compression is fully transparent - programs, games and files can still be accessed as normal, and show up in Explorer as they normally would — they'll just be decompressed into RAM at runtime, staying compressed on disk.
Options
By default, the program runs Compact with the XPRESS8K algorithm active. This provides a good balance between compression speed and size reduction. The default that Windows uses is XPRESS4K which is faster but compresses less.
The options available are:
- XPRESS4K: Fastest, but weakest
- XPRESS8K: Reasonable balance between speed and compression
- XPRESS16K: Slower, but stronger
- LZX: Slowest, but strongest - note it has a higher overhead, so use it on programs/games only if your CPU is reasonably strong or the program/game is older.
Additional Notes
In my testing, using any of the XPRESS modes has no discernible impact on CPU performance when the compressed program is run (Using an i7-6700HQ). Here's the output tests for Adobe Photoshop:
However, if your processor is especially old, you may find that performance is worse when folders are compressed with 8K and 16K. Use 4K instead. Despite this, I've successfully tested it on an i3-370M from 2010, and it had no issues with performance on any of the compression modes.