I purchased a set containing 4 of these Anchor Hocking Fireking Custard Cups a few decades ago.  It seemed that every household  had at least one set of these.  To me it was part my baking and cooking needs just like everyone has a set of measuring spoons and measuring cups.   I mostly use them for making one of the packages of pudding.  I can fit 3/4 cup in each one which is 6 ozand it accommodates the full package that is made with 2 cups of milk.  I like that they are clear glass.  The glass is very thick and I have not chipped any in the many hundred times they have been washed and used.  The logo, Anchor, is on the bottom  of each with the size.  These were made in the USA, are up to 425 degrees oven safe and microwave safe but not to be used in a broiler or stovetop having high direct heat.  These glass cups are very easy to clean.  Since they are glass, odors will not absorb like plastic-ware nor will they stain.  Mine still look like new. 

These custard cups can be found at any store that sells bakeware, kitchen assessories.  Both Anchor and Pyrex make good quality bakeware so either would be a good choice if I needed to replace mine.  I also noticed a few other brands that sell custard cups.  These custard cups come in different sizes; 6, 8 and 10 oz. in sets of 4.  Prices may vary per store but in average they go for under $6 for the set. 

While mine did not come with plastic covers which I've noticed they have now, I don't miss the covers.  Whatever I use them for, it is mostly not going to be stored for long.  But when I make pudding I use a cover each with a small strip of wax paper while it's cooling and never would use a tight plastic cover. 

I like to call these both cups and bowls.  I use them for serving small portions of foods such as mixed fruit, jell-o, pudding or ice cream.  They are so versatile I also use them to melt butter in and also to blend sugar and cinnamon when using it to pour over my apple coffee cake I make from scratch.  The use for these are endless with an everlasting durability.  They are small, heavy duty glass, making them practical and useful for a variety of individual uses.  You can also freeze foods in these but I never have because of the small size.  I would prefer to use a freezer bag.

They are also handy if you're having a make your own sundae at your home to fill with nuts, sprinkles, chocolate syrup and cherries.  There's no worry that the cup will get knocked over and spilled because of the type of glass with the flat bottom.

If you watch the food network on TV you will notice some cooks will use as many as 10 of these.  They will use one for every pre-measured ingredient they are using in their recipe especially for herbs, seasonings and anything that will hold under a  few tablespoons.  They make the recipe look so easy with all the ingredients sitting in these cups ready for the camera to capture the blending of all the additives so that they can make a dish in a few minutes.  I don't use mine for holding several individual spices like that but I must say it looks nice to have everything measured before making a meal in these cups.  They make a nice presentation when showing someone how you make a dish with many seasonings. 

I think everyone should have at least one set of these in the size that suits your needs.  They are heavy making them durable and clean easily.  I would rather use these than a small  plastic bowl.  While these are not fancy for entertaining, they are practical and durable for everyday use.  Whenever I need a small mixing bowl or a cup to hold small amounts of anything to heat in the microwave I always reach for this.  I'm sure that are many other uses based on each household's personal needs. 

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