Halcyon is described as 'A twitter-like web client for Mastodon and Pleroma'. There are more than 10 alternatives to Halcyon for a variety of platforms, including Android, iPhone, Self-Hosted solutions, Mastodon and Online / Web-based. The best alternative is Tusky, which is both free and Open Source. Other great apps like Halcyon are Whalebird (Free, Open Source), Amaroq (Free, Open Source), AndStatus (Free, Open Source) and Pinafore (Free, Open Source).
Tusky is a client for Mastodon, a free and open-source social network server. Share words, photos, and videos with folks! Mastodon is decentralized, meaning anyone can run Mastodon and participate in the social network seamlessly.
AndStatus is an Open Source low traffic social networking client with tree-like threaded conversations. It supports different Social networks, including GNU social (StatusNet, e.g. Quitter.se, LoadAverage, etc.), Twitter and Pump.io.
Toot! is a client for the Mastodon social network. It is beautiful, and full of character and whimsy. What makes Toot! special? - It is delightful. It is full of beautiful design, animation, amusing details and hidden treasures.
Mast is a beautiful Mastodon and Pleroma app built with iOS design guidelines in mind. It’s as feature-packed as it is gorgeous. With customisable content and themes, it’s most definitely the perfect choice.