| lsz | Litestep Theme File |
| lt | Moltemplate Data File |
| lt2 | Poser Light Data |
| lta | Monolith LithTech Game Engine Data |
| ltc | Linguistic Tree Constructor Data |
| ltcx | Linguistic Tree Constructor XML Data |
| ltd | HPE Library and Tape Tools Support Ticket |
| ltd | LivingTime Data File |
| ltf | Frogans Short-cut |
| lth | Roxio Label Creator Style Data |
| lthmb | Adobe Presenter Audio Thumbnail |
| ltl | TwoTowers LTL Formula |
| ltn | Carlson Survey Lot Network File |
| ltt | HP Library and Tape Tools Log |
| ltz | Poser Compressed Light Data |
| ltz | Poser Light Data |
| lu | ThoughtWing Library Unit |
| luacodec | Reason Remote Lua Codec Data |
| luar | UltraDefrag Lua Report |
| lucidcolorset | Lucid Colorset Data |
| lucs | Amaya Tools Data |
| lucy | HTC Scribble Note |
| lud | Altair FEKO LU-decomposition Data |
| lud | CARE-S InfoWorks Land Use Data |
| lud | ABBYY Lingvo Dictionary User Dictionary |
| lue | Norton LiveUpdate Log |
| luh | ARINC 615A Load Upload Header |
| lum | Luminous Schedule File |
| lup | ARINC 615A Load Upload Part |
| lup | OzWin Library Update File |
