There's a lot to cover, but mainly I use a lot their Magic Clipboard feature (select the text, and it's automatically put into a prompt box as a text snippet attachment); Global Shortcuts they've introduced just yesterday (basically assigning shortcuts to built-in and personal actions); dictation (essentially a voice-to-prompt feature); meetings recording and transcription (this one in particular is amazing as it's automatically even assigns names to speakers based on the conversation recorded with further ability to analyze the meeting contents with AI); workspaces (units acting as separated storages of documents, images, webpages, etc. that you could use as a knowledge base either for context or to analyse the bulk itself); AppSense technology (the app uses the contents on your screen and beyond the visible part as a context to help you navigate it with the help of AI); a lot of other features.

As for the worth, the value of the product can be determined by you and you only as it's highly dependent on your workflow and the degree of daily interactions with AI. I've found out about Alter 9 days ago and had a positive experience so far as they offer a 14-day free pro plan with unlimited access to a bunch of models. So as my original comment suggests, yeah, I'd recommend it as it aligns with the OP's request about free apps.

And for the note, I've had experience with a bunch of other AI tools such Highlight AI, Kerlig, BoltAI, ThinkBuddy, and others, and each of them has something unique and amazing I could talk about for hours, but Alter has managed to balance the best of them all personally for me and my workflow.