A very simple online pain tool. No downloading needed and it's completely free. It doesn't have nearly as many brushes and such as Photoshop or other paid for paint tools, but it gets the job done alright. The only big con in my opinion is that the amount of layers you can have is rather limited.

Name: Ibis Paint X

Free/Paid: Has both
URL: Its an app for mobile devices and doesn't have one?

Review/Features: Uh, its supposedly the most well known, common and favourite drawing app for mobile devices, having multiple features including adjustable/editable brushes of multiple types, layers, clipping masks, locking layers, adding text and images, different preset backgrounds and designs, and features to edit the image such as filters, canvas splits, resizing, cropping and such. The purchasable one has pretty much everything while the free one has a lot less brushes and some missing features. This is not a great review though, someone do a better job!

Pixlr has both a free and paid version, it's a relatively new update :)

Name: Ibis Paint X

Free/Paid: Free

Review: A really useful app, over 100 brushes, and you can import and create more, and can be used for all devices other then tablet. (I am pretty sure) no login needed, and you can save images to the cloud if wanted not sure what else to say.

Name: Drawpile

Free/Paid: Free

URL: https://drawpile.net/

General Review: Drawpile can be used both online and offline but is more fun with friends. There are a number of thriving communities that you can join, and a number of them specifically host roleplay boards where you can draw-roleplay, sketch, hang out, or what have you. Having an account is optional, though some community boards may require it for unlocking access to some of the tools; community boards may have their own moderators to prevent griefing. The mods and members can always help answer any questions you have, also. Drawpile is built around collaborative artwork, like many online sites, and you can host your own boards on it, too.

Features: The tools in the program itself are quite simple, both in terms of layout and number of brushes available, but the brushes do have customization settings. The smudge engine in the program is my absolute favorite. The docker locations are customizable. It is not mobile or tablet-friendly, unfortunately. [Edit: posted prematurely,] As mentioned before, the program is online and offline, as you download it onto your computer to use it, and can either open the program to use it on your own, or connect to a public or password-invited group through the opened program.

If there is anything else that's been forgotten, I'll add it in the future. Happy painting!