Accounts are local to the instance they are created on, so unless Lemmy provides an API the mastodon client can talk to (which AFAIK it doesn't) you can't use one client with a different server. Posts and other things (likes, videos, images, comments, etc) are federated between instances so you will be able to see posts. How the different apps (Lemmy, Mastodon, Pixelfed, Peertube, etc) interpret and choose to display those, as well as how they interact with those (e.g. allowing you to comment on a comment vs only on a post) vary across the different offerings.
Lemmy
Everything about Lemmy; bugs, gripes, praises, and advocacy.
For discussion about the lemmy.ml instance, go to !meta@lemmy.ml.
Thanks! Seems like the official Mastodon app lets you search and follow users on here, as well as comment on posts, but not make posts or follow communities… interesting.
Edit: actually, looks like you can follow communities. They show up as reblogs/retweets on the original post owned by the user. This opens up some interesting possibilities, if all you want to do is follow specific communities and comment on them.
That's not supported at the moment I'm afraid. The features of Lemmy and Mastodon have an overlap, but differ in meaningful ways, e.g. you can't downvote from Mastodon (apps).
Lemmy is still in the early stages of development and I'm sure the app-ecosystem will improve!
They have a completely different UI, so I don't think that's likely, but I might be wrong.
Lemmy and Mastodon servers are capable of speaking to each other using the ActivityPub protocol, but they present substantially different APIs and user interfaces to the end user. There is no way to use a Lemmy app to log in to a Mastodon instance, or vice versa.
Mastodon has no concept of communities whatsoever, nor any features which derive from them (like community level moderators, or directing your comments towards various communities instead of your timeline). It doesn't distinguish between "posts" and "comments." Its moderation / reporting system works very differently. Media uploading, alternate text, etc work very differently. and so on and so on.
Comments / replies can be seen/shared from one platform to another, but the various ways users interact with them are quite different.
@AineLasagna
I was able to create a post from Mastodon: https://mander.xyz/post/1029976
I don't _think_ it's an app feature, but I'm using Fedilab. Comments work as expected.
It's not perfect, but it's working for me. 🤷♂️ I haven't seen faves translate to upvotes, but I've not done a bunch of testing with that.