We have two different products for reading and flashing Atari Lynx carts. One uses a Raspberry Pi (not supplied) and the other is a USB device that you can drag-and-drop ROMs to/from. Note that a flashable cartridge is required for writing ROMs, original Atari cartridges cannot be written to.
See this page for information on how to set up and use the Raspberry Pi device. Also check this out - How to make a homebrew Atari Lynx cartridge.