I looked for another thread that might have asked the same thing but couldn’t find one.
Like Wordpress has Jetpack for automatic blog post sharing via Twitter and Facebook, does Grav have something similar with a plugin? Or is there a best alternative way to do it?
@lukealexdavis, You may try searching on https://getgrav.org/downloads/plugins and see if there is one…
If you are using Admin to create your posts, you could build a plugin that uploads a new post to Twitterer/FB when the post gets saved. If you are not using Admin, AFAIK there is no ‘event’ you could listen too to trigger a plugin to do the upload, which makes the logic a bit more complicated.
I already looked through the plugins but couldn’t find one.
I’m also not knowledgeable enough to create my own so I guess I’ll wait to see if anyone else does it.
Using the Add Page by Form Plugin you can create blog posts from the frontend. After the page with the blog post has been created the plugin fires a “onAddPageByFormPluginAfterPageSave” event. As @anon76427325 wrote another plugin could act upon that event and pass the post on.
And remember, knowledge is something you can gain 
To add to my previous comment…
A plugin could respond to event onPageContentProcessed. This event is only called when a page is not yet cached after creation or update. The event is fired, whether the update is made by Admin, text editor or anything else.