simple

What advantages/disadvantages does it have over Lemmy?

It has more features, such as flairs, a way to move communities somewhere else, the ability to see comments from all crossposts, multi-communities, and it has a much faster development pace. The UX still needs some work, but that can be improved over time.

From a technical perspective it’s made with Python which is much, much easier to use than Rust and attracts more contributors. From what I understand it’s easier to host too.

Can I see and interact with PieFed instances and communities from a federated Lemmy instance? What about the other way around?

Yes and yes.

Is there a way for people to migrate an account from Lemmy to PieFed? What about the other way around?

You can export your Lemmy account settings and import them to Piefed, but not the other way around.

What android app options are available for PieFed?

https://interstellar.jwr.one/

Wikipedia has a lot more donors, but also their costs are probably cheaper than Signal. They mostly host text and decently compressed images, Signal uses way more bandwidth and people share high quality videos and other huge files. The servers are very expensive, there were articles estimating their cost to be around $50M per year.

Makes sense., something as huge and expensive as Signal can’t run entirely on donations.