The OpenTX community is a thriving and exciting place to be. Many Third Party add-ons work with the radios. This list is probably incomplete. If you think your (or someone else's) add on belongs here, do not hestiate to tell us.
LView - https://github.com/RealTadango/FrSky/tree/master/LView - Lua log viewer for FrSky Horus with OpenTX
LuaPilot - Telemetry screen for Arducopter
Open-Tm - Telemetry screens mainly for models with acclerometer (includes Betaflight with telemetry)
Beware that these sound packs might not be update with SD card conents and might be missing some sound files from newer releases.
Amber Sound pack - https://www.dropbox.com/s/3t7p9t6ykufhsfx/Amber22.rar?dl=0
"Mia" Taranis Voicepack (commercial - 5 USD)