Opening Sln File
Sln extension is associated with Visual Studio Solution File. You can try to open sln files with Microsoft Visual Studio.
It is a text based file which provides tidy work during the software creating process in Microsoft Visual Studio. Sln files are similar to Windows program grouping files (.vbg) and these files are used by Microsoft Visual Basic. You can try to open sln files with Microsoft Visual Studio. To get detailed information about the system, you can get free software from that link.
Opening methods of Sln file
Microsoft Visual Studio
Links to opening Sln file