Basically any device or thing that has an internet connection can publish information about itself so that it can be consumed externally. For example if you had a BeagleBone microprocessor monitoring temperatures and you wanted to share those temperatures with other people or machines on the cloud, you could do it easily with dweet.io. It's basically a really simple pub/sub platform.
No promises yet, but we plan on offering paid plans that could offer SLAs on latency. Although I will say we architected it from the get-go to be high throughput and low latency— it's all using redis in-memory on the back-end.