The best alternatives to Thread Portal are Refined Twitter, Twitter, and Life on Twitter. If these 3 options don't work for you, we've listed a few more alternatives below.
Refined Twitter improves the Twitter experience by removing cruft and adding useful features. Available for Chrome, Firefox, Opera. Some of the best features are: Embedding linked Instagram photos directly in the tweet, syntax highlighting of code blocks, auto-loads new tweets in the stream if you're scrolled to the top, removes promoted tweets.
Turn ideas into posts, posts into threads, and threads into followers. This will help you stay consistent, learn a lot and grow your account. Also, it includes an analytics page so you can a feel to how your tweets are doing.