| bson | Binary JSON Data |
| bsr | Bacula Bootstrap File |
| bsw | Microsoft Office Business Scorecard Manager Workspace |
| bsy | VTrain Learning Card |
| bt | Binary Terrain Data |
| bt2 | Batch Barcode Maker Data |
| bta | Bend-Tech v3 Assembly File |
| btax | Bend-Tech v6 Assembly File |
| btf | NationsBank Check Image |
| bth | TimeZero Bathy Recorder Data |
| btif | NationsBank Check Image |
| btk | CLwin Tekton Database |
| btmsp | MALDI BioTyper Main Spectra File |
| bto | Bryce Tree Object |
| btp | Bend-Tech v3 Plate File |
| btpx | Bend-Tech v6 Plate File |
| btr | Btrieve Database |
| bts | Blaise Specification |
| btsearch | BitTorrent Search Engine Data |
| btskey | BitTorrent Sync Data |
| btskin | BitTorrent Skin Data |
| btt | Microsoft BizTalk Tracking Profile |
| bttx | Bend-Tech v6 Part File |
| btv | AppleTalk Desktop Database |
| btw | Bartender Format Data |
| btx | DB/TextWorks Database Term and Word Index |
| btx | Bend-Tech v3 Part File |
| btz | Helix Toolkit Compressed BT Data |
| bu | Pegasus Mail BU File |
| bub | PhotoBubble Image Data |
