General Websites/Programs
Nitrome
UK-based indie game studio which has developed 100's of beloved flash games during 2000's and 2010's. Many of their games have been converted to Html5, but you'll need to download Supernova to play a good chunk of their library still.
Cool Math Games
Another beloved 2000's flash game site. Hosts Html and flash games.
Itch.io
A website home to thousands of indie games, books, zines, resources and more.
Gamejolt
Another website like Itch.io with a bigger focus on games.
Pony Town
My Little Pony based MMO where you can play as a pony and interact with other ponies.
Flashpoint Archive
Program you can download to play thousands of archived flash games that otherwise would have been lost to time.
Game Reccommendations
Nitrome
Fault Line
(Puzzle) (SFW)- Puzzle game where you play as a space bending robot who can fold reality with his hands. (One of my favourite Nitrome games lol)
Blast RPG
(RPG) (SFW) - Interesting RPG/cannon-firing, distance game hybrid.
Steamlands
(Strategy/action) (SFW) - Steampunk tank-fighting game where you can build your tank out of scraps from enemy tanks. (another one of my fav Nitrome games lmao)
Rush
(Racing) (SFW) - Racing game where you play as gravity-flipping robots. (another fav of mine)
Gamejolt
Anthology of the Killer by thecatamites
(Horror/comedy) (CW: Cartoon blood, gore and violence) - A complete list of games from thecatamites' "Of the Killer series", which can be downloaded from Gamejolt. (My favorite ones are "Ears of the Killer" and "Heart of the Killer".)