You checked 7-zip. It has a full SDK, with sample sources and great functionality. This is open source and free :) Take a look here
Nice shell around SevenZipSharp . Using an example:
SevenZipCompressor compressor; compressor = new SevenZipCompressor(); compressor.CompressionLevel = CompressionLevel.Ultra; compressor.CompressionMethod = CompressionMethod.Lzma; compressor.CompressionMode = CompressionMode.Create; compressor.CompressFiles(archiveName, files2Add.ToArray());
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