Moonlight is software that lets you stream games from one PC to another (I'm not talking about streaming to youtube or Twitch btw). For example, a common use case would be to stream from your Desktop to a laptop or a raspberry pi thats hooked up to your TV. So you can then play your game from the raspberry pi.
In particular, I would like Moonlight ported https://moonlight-stream.org/, it's open source and already has a portable version, so I'd think it should be easy enough to add to portableapps.