Element is just a client that can connect to the Matrix which is federated and decentralized just like Lemmy. Element is heavily promoted because element is the most well-developed client out there (made by the same people behind the matrix so they get the new features first) but far from the only one.

Regular element is free on all operating systems including windows, linux, android, etc. And there’s even a web version.

And just like Lemmy you can register on any instance and communicate with any other (federated) instances. Matrix.org being the biggest one but there are countless and you can even self-host.

If you’d rather use another client you can use any of these listed here: https://matrix.org/ecosystem/clients/

To use Element on the web you just need to go to:
https://app.element.io/