Converting PNG to ICO (Icon) format can be accomplished using various offline tools、Here are some popular options:

For Windows

1、IcoFX: A popular and userfriendly icon editor that allows you to convert PNG to ICO、It offers a free version with basic features.

2、GIMP: A free and opensource raster graphics editor that can also handle icon creation and conversion、To convert PNG to ICO, open your PNG file in GIMP, then go to `File` `Export As`, choose Windows Icon as the file type, and you're done.

3、Paint.NET: Another free image editing software for Windows that supports converting PNG to ICO with a few simple steps、Open your PNG file, then use the `File` `Save As` option and choose ICO as the file type.

4、XnConvert: A free tool that supports batch conversions、You can add your PNG files, select ICO as the output format, and convert.

For macOS

1、GIMP: Also available for macOS, GIMP provides similar functionality as on Windows、Open your PNG file and export it as an ICO.

2、Preview: The builtin macOS Preview app can open PNG files, and with a little trick, you can save them as ICO、Open your PNG, then go to `File` `Export`, and in the dropdown menu, select Icon (.ico).

3、IconEdit: A dedicated icon editor for macOS that allows you to create and convert icons.

For Linux

1、GIMP: Available on Linux as well, GIMP offers the same functionality as on Windows and macOS.

2、ImageMagick: A commandline tool that can be used to convert images, including PNG to ICO、You would use a command like:

convert input.png output.ico


3、Krita: A free and opensource painting and image editing software that supports a wide range of file formats, including ICO.

Online Tools (if an offline tool isn't strictly necessary)

If you're open to using an online service for a oneoff conversion, websites like ConvertICO, ICO Convert, or OnlineConvert allow you to upload your PNG and download it as an ICO file.

Commandline Tools

For those comfortable with the command line, tools like ImageMagick (mentioned above) offer crossplatform support and can be used on Windows, macOS, and Linux.

Choosing the Right Tool

For Casual Use: If you only need to convert PNG to ICO occasionally, using an online tool or a builtin image viewer/editor might suffice.
For Professionals or Batch Conversions: If you're working with icons frequently or need batch conversion capabilities, consider downloading a dedicated image editing or conversion tool.

Always ensure you're downloading software from reputable sources to avoid any potential malware issues.