A simple web app demonstrating how text sounds in different TTS voices.
Choose from 500+ voices from Amazon Polly (via Streamlabs), TikTok, CereProc, IBM Watson, Acapela, Oddcast, ReadSpeaker, Google Translate, iSpeech.
Polly voices can be used for testing how Twitch.tv donations will sound as many streamers have TTS enabled via Streamlabs or StreamElements for this.
Also you may wish to check out the "TTS Dossier" for some entertaining ideas.
Finally, here's a list of characters explaining how they are pronounced (specifically by Brian).