BucketBot.io
Upload pics and files to Amazon S3 directly from Slack
8 Alternatives To BucketBot.io
Bashupload
Upload files from command line to share between servers
DropPy
Automate anything via drag & drop using Python.
Dropzone
If you want your file uploads to work even without JavaScript, you can include an element with the class fallback that dropzone will remove if the browser is supported.
Send To My Cloud
Let your users upload files to your cloud storage
Shubox
Simple, fast, customizable uploads from your web app to S3
Uploader Window
Easy File Uploader for your websites and apps
Uppy
The next open source file uploader for web browsers
imgix
Real-time Image Processing. Resize, crop, and process images on the fly, simply by changing their URLs.