Three I know about are the TWSBI Eco and Diamond, and Pilot’s disposable Vpen. They’ve already been mentioned elsewhere in this thread.
Beyond those, do research. Fountain pens drying out is a major problem that catches newcomers off-guard. When you can buy EnerGels for peanuts, fountain pen manufacturers really need to up their game to stay remotely competitive with other pen types. And many don’t.
You do need to cap fountain pens because the inks are water based.
If you need to take quick notes and drying out is a problem because the pens are uncapped and capped a lot, get a Lamy 2000, vintage (not new) Parker 51 or a Pilot Vanishing Point. The first two have slip caps and hooded nibs so cap and uncap really quickly and don't dry out due to the hooded nib. The Vanishing Point also has a hooded nib but you click it like a ballpoint pen to expose and hide the nib. Also don't use quick drying inks.
If drying out is a problem because you don't write frequently enough, there are two solutions. Solution 1: Buy a Platinum (Preppy for low end, or 3776 higher end). It has a really good cap. Both will take a long time to dry out. Or even better, write more frequently.
The Kaküno is a small pen, intended for the hands of children. But it is outstanding at that price point, and it uses the same cartridges/converters as the Metropolitan.
My kids have them and will use them until they outgrow them.
