Tipping features I've seen on Twitch:

- Put a message on the screen (as JB mentioned)

- Request to play a youtube video (longer videos cost more)

- Tip to decide what a streamer should do in a game

- Tip to get the streamer to play a certain game

- Tip to be number one tipper (people seem to care very much about this on some Twitch streams)

- Tip to get artist or musician to sing/play certain songs

- Tip to feed the god damn chickens (already done for a long time with BTC and LN)

There are probably many other tipping activities I'm forgetting. If tipping/donations doesn't work on your platform, you're doing it wrong (or don't have the correct, or enough, users/audience).