Tibbo Composite Uncompressed (TCU) files contain multiple data sections: TiOS firmware, compiled Tibbo BASIC/C application (optional), and even the internal firmware of the WA2000 Wi-Fi/BLE add-on module (optional)!
.TCU files may be used for updating programmable Tibbo devices in a variety of ways. Chief among them is Over-the-Air (OTA) updating via the Bluetooth Low-Energy (BLE) interface of the WA2000 Wi-Fi/BLE add-on module. Only the devices that are compatible with this module support OTA updates. Such devices are marked with an asterisk in the Device Platform drop-down (naturally, the WA2000 must actually be installed for OTA updates to work). You will need a Tibbo Updater iOS or Android app to perform the updates. The procedure for performing BLE OTA updates is described here: http://docs.tibbo.com/phm/index.html?ml_ble.htm.
TCU files may also be utilized by a Tibbo BASIC app containing code for self-updating the device. An example of such an app is a Tibbo Self-Updater app published here: http://tibbo.com/programmable/applications/tibbo-self-updater.html. Self-updates do not depend on the WA2000 add-on, as they do not dictate any particular method of receiving the TCU file into the device.