The Bluesky Crossposter is a python script that when running will automatically post your bluesky-posts to mastodon and twitter, excluding responses and reposts. The script can handle threads and image posts, including alt text on images.
To get started, get the necessary keys and passwords and enter them in auth.py. Then fill in your paths in path.py. Finally set up a way for the code to be run periodically, for example a cronjob running every five or ten minutes.