C++17
GUI: wxWidgets (c++)
Databases: wxSQLite 3 (c/c++)
Parsing JSON: JsonCpp (c++)
Parsing XML: wxWidgets (wrapping over libexpat)
Cryptography (checksums, asymmetric encryption) CryptoPP (c++)
Archiving at the moment – zlib, more efficient in terms of compress ratio lzma2 (liblzma) (c/c++), is not yet available in the release, due to the fact that this format is not a container for several files, but a compression algorithm and it is necessary to collect all files into a single container before compression (for example tar), and this is an extra waste of either RAM memory or disk space. It was tested in development, maybe someday, after some R&D it will get into the release. At the moment I don’t plan to use 7z as a separate dynamically linked (dll) library (or just CLI to 7z.exe as in some similar programs).
Some Win32 Api, for Windows specific features.
Drawing some graphics in offscreen bitmaps and output to DC using Direct2D or GDI.
Working with the Windows registry, file system, IPC (Inter-Process Communication), configuration files, sound, network — wxWidgets (c++) built-in classes.
Graphic icons — vector svg, convertible in runtime to the desired format.