For Photoshop:

1) Photopea (quite brilliant for most of the things photoshop can do)

2) paint.net for not too advanced edits

3) Krita

For After Effects:

1) Natron

2) BlackMagic Fusion

For Premiere Pro:

1) DaVinci Resolve

2) KdenLive

For Illustrator:

1) Inkscape

2) Graphite

Please note that most of these are not feature for feature replacements, but for the most part and most common tasks, they are very good offerings.