You mean one that allows logging in and posting to Twitter aka X, without a significant fee? Not to my knowledge. Lately Elon and co. have been working to make third party clients completely impossible to develop, so it's either use the official app, use the website, or quit Twitter.
If you just want to browse Twitter, I don't know of any options for that either, but keep an eye on Nitter; currently it does not work, but they're apparently working on a way to work around Twitter's latest changes.
At this point I would use Mastodon and follow Twitter users on there through the bird makeup instance. It basically creates mirrors of Twitter accounts so you can see what they post (but you can't interact). It'll only add new posts while somebody's following them though, so you might not have past posts if nobody has followed them yet.
Another thing is some people are posting to both now or have switched entirely. You can see who you follow on Twitter is using Mastodon with this site https://fedifinder.glitch.me/
I've had a Twitter acct for a long time, and I still use it. I've curated my feed to contain virology/epidemiology specialists, independent journalists, and eye candy. I have 2 ways of finding people to follow. 1. When I'm reading on the internet and find something I like, I look to see whether they've got a Twitter acct. 2. If someone comments intelligently on a good post, I check their profile. If they post stuff worth reading, I follow them. As for eye candy, I'm attracted to ancient stuff. There are several archaeologists who post.
I've "followed" several people from Twitter on Mastodon. I can't see them in my feed, but I can view the list of people I've followed and click on them. For now, their Mastodon posts come from bots that echo their Twitter posts. It looks like everyone's hedging their bets. If I need to leave Twitter, I can still access most of the info I'm used to getting from there.