NOTE- I DID NOT READ ANY OTHER POSTS SO PLEASE DO NOT DOWNVOTE FOR REPOSTS.
First game - Airmech. With low end stuffs, you can play this free game that is partially a MOBA, being that you battle with 'transformers' and create units to help fight with you.
TF2- Pretty much everyone knows this one, free
Terraria- 9.99 game that you can get for more like 4.98 buying CS:GO keys and trading them for it on sites like steamgifts.com terraria is a game which is basically 2D minecraft, you run around and fight mythical monsters, while building your base and progressing through the game. This is a plat former and I have 200+ hours on it, highly recommended.
Flash games. Basically all free, not on steam usually, but you can check www.kongregate.com
which is a highly trusted flash games website, considering it is owned by GameStop. I suggest you check it out, which a list of some games I used to love playing.
Anti-Idle the Game - Crappy game, but highly addictive. It is another one of those idle games, but not one where you just have to click click click.
Realm of the Mad God - Very mixed reviews, check it out at your own risk, considering it is partially p2w, but usually everything is legitimately obtainable. Also on steam, not just flash game.
ShellShock Live 2 - Great game in which you master physics, to shoot your tank shots in the air, to hit other tanks. Multiple game modes, many, many unlockables. And a bundle of fun, but I can't play it for more than a few games, considering how grindy it can be. This is a flash game, but also a very unpopulated version is on steam, too.
A fun FPS on steam, maybe not so low-end than others, is Dirty Bomb. It is a first person shooter in which there is elimination mode, and some other modes that relate to cs:go. You gain coins to open card packs to unlock more specialists to use. Fun game, but once again, quite grindy.
CS:GO - Many people know about this game, but if you know about it, and think you can't run it, you seriously need to buy this game on a sale and check it out. It is a beautiful realistic FPS, in which you can't aim down sites with most weapons, and there are skins, which are the currency of CS:GO. I suggest you try it out, because most people who own this game have 400+ hours, and it is either you like it or you hate it.
I hope you enjoyed this list, considering I made this on my iPad, it may be lacking some punctuation and spacing. Please consider this post and comment if you have any questions about it, and I will answer it if I can, have a good day!
Some other games that are good on low end pc's, but i do not have a description or background with: Undertale, Dwarf Fortress, Robocraft, Lovers in a Dangerous Spacefime, and Legend of a Dungeon.
If you have any suggestions, please let me know below, and a description of it would be great!