well for classic i would suggest playing emulator start from PSP or lower (PS2 not very friendly for low end)
but if you searching for windows games i would suggest start from Moriya and start from original Touhou series i could say every one of them work perfectly on low end but i haven't play all but fan game here is worth it too like Magical battle arena next (also Sky Arena too but lack of lower resolution but still run fine mostly lag on bamboo forest)
here quick name of mostly stuff i get from here : Mystical Chain, Rhythm Carnival, Touhou Soccer (both), Pocket war, Touhou labyrinth 2, Bullet report, Fantasy maiden war series, Genso rondo, Koumajou densetsu, Shoot shoot Nitori.
I could say all of them run fine on Celeron with 2gb ram but if you want other one i suggest you can find it on Youtube.