Below are some recommended sites for discovering small, niche, and/or free games:

• itch.io, a large indie game storefront, home to game jams, large indie publishers, comics, and more weird little games than you could hope to shake any stick at
• GameJolt, less a storefront than itch, GameJolt has a very active player community aspect and a lot of interaction with developers
• Glorious Trainwrecks, a friendly, open site with an active community that creates (mostly) quickly-produced games around events. A great site for discovering personal, unique, and even bizarre games.
• Freem! (Japanese), a long-running site with thousands of free (mostly) Japanese games of all genres
• FreeGame Mugen (Japanese), much like Freem! with some overlap and some unique games