WireShark Capture file conversion and repair
These tools convert between different capture file formats.
PcapNG.com Free online service that converts Pcap-NG files to plain libpcap (PCAP) format.
ProConvert convert capture files between different formats - some that Wireshark currently doesn't support (closed source freeware, unsupported and noted as buggy by vendor, registration and WildPackets maintenance contract required, Win32 only)
These tools attempt to repair damaged capture files as much as can be done.
pcapfix can repair corrupted or truncated capture files.