If all you want to do is to decompress mission PBO files, decrypt official MISSION.SQM files or compress mission file directories back into PBO files, you're at the right place! If you need more than that you'll have to browse the major OFP editing sites.
UnPBO V1.5 - both decompresses PBO files and decrypts its MISSION.SQM file in a single swoop. Supports OFP: Resistance PBO files, too!
PBOTool V1.01A - unpacks and repackages mission file directories from and to PBO files. Supports subdirectory compression, which is useful for campaign and addon makers.
Stellar Addon Compiler - Compiles your addon folders and files into ready-to-play PBO files.
DePBO - decompresses mission PBO files.
Unpack-SQM - decrypts encrypted MISSION.SQM files. If this doesn't work for you, give DeSQM a try.
MakePBO V1.1 -compresses mission file directories back into PBO files. Supports subdirectory compression for campaigns and addons.
StuffPBO - the original PBO compression utility. Does not support subdirectory compression.
CPP2BIN - converts CPP files to BIN files. Handy for you addon makers out there.