bbx10 on the adafruit forums. bbx10 developed the Ascii to HID translation function. A massive thanks - the code is currently mostly his. He also worked out some of the early problems on speed issues we were having. You can read the full thread here.
HID-Relay from juancgarcia. Not really spent much time looking at this - but looks neat. Converts hardware keyboards to Bluetooth.
232Key - Converts Serial devices to Keyboard. Kind of the other way round to what we want.
BL_keyboard_RPI. Turns a Pi into keyboard emulator
ESP32_mouse_keyboard. Uses a ESP32 as a mouse/keyboard over serial. Very similar idea. (See issue 39for details about this in relation to using VNC (TY @RoganDawes)
MacroServerMac was an attempt to create a Mac Port of "MacroServer" developed by JabblaSoft for MindExpress . This is a protocol for communication over a TCP/IP stack. Its pretty nice - but if you are in a school or business allowing others machines to access the network in this way is often restricted. It can also be pretty flaky
Dynavox used to make the AccessIT. A similar idea but using infrared rather than radio/bluetooth. It was pretty expensive but a lot of people loved its simplicity. More recently they have brought this back to life with AccessIT 3. Note it only works in Snap software - and not for any device. Just another windows device. You also need a USB port on the device you connect to.
The AAC world has been trying to create standards for this for years.. and some have succeeded. Check out AACKeys and the "GIDEI" protocol - which now feels a little outdated but a great attempt at standardising communication between AAC devices and other systems over serial.
the Buffalo BSHSBT04BK was pretty neat. You can still get this in Japan and does a very similar job
The IOGEAR KeyShair (now discontinued) looked like exactly the same dongle - but with different software.
Both of these products though failed to respond to software (on-screen) keyboards reliably.