Try these if you want help knowing how to rewrite fractions with different numerators and denominators, or understanding why 2/3 is the same size as 10/15.
Equivalent Fractions by NCTM Illuminations helps show why some fractions are the same size as others. I recommend using the square model rather than the circle. Try "Build Your Own" with 3/4, 2/5, 1/6, 2/3, 5/8, 4/12, etc. Equivalent Fractions by Mark Weddell is similar.
Melvin's Make a Match could work as a review game after you work with equivalent fractions for a while. (If you hover over a piece in this game, it shows it a little bigger.)
Fractions with Pictures
In Fraction Flag, you choose the proportions to represent some colors in a flag (for example, half one color and half another color), then design a flag that has those proportions. The design is limited to halves and quarters (fourths).
Fraction Models (by NCTM Illuminations) is, frankly, somewhat boring, but it's a great way to explore connections between fractions, mixed numbers, decimals, and percents with a visual representation.
Fraction Sizes: Choosing Smaller or Larger Fractions
Dolphin Race (Comparing Fraction Size) was definitely a crowd favorite among sixth graders in 2015. It feels competitive, but gives you time to think, and there are two different levels.
Fractions Ordering Game asks you to place fractions in order of size. If you get some wrong, it gives you another chance to rearrange those. There are three levels of difficulty.
In Fraction Game by NCTM Illuminations, use equivalent fractions and estimation of fraction sizes to "play" fraction cards on fraction number lines. (Read the instructions first.) Play several times. How few cards can you use? What are good strategies to reduce the number of cards you use?
Fraction Feud on Calculation Nation (log in as guest, or at home you can set up an account) is fun for fraction masters who like strategy games. Make a fraction SMALLER or LARGER than the one you’re “jousting” against. Try to figure out which cards are generally best to use or keep for later.
Various Other Fractions Activities
Sheppard Software Fraction Games include a lot of "Splat" and "Mathman" (Pacman-like) games about improper fractions and mixed numbers, equivalent fractions, adding fractions, subtracting fractions, and a LOT of other choices.
There are some challenging Fractions Activities on NRICH, a British math (they call it "maths") site with a lot of incredibly creative games and lessons. If fractions are easy for you, go here and explore, and let me know which things are interesting!
IXL Fractions Activities is a for-profit site, but it lets non-members practice a few minutes. The activities are quite repetitive, but you may like them as a sort of quiz/self-check.
Speedway (Adding Fractions) on Math Playground is good mental math practice for adding and reducing fractions, if you're already comfortable with that. Speed is a big part of this one.
If you already know about decimals and percents (which we will learn more about later this year), you might like Fraction/Decimal/Percent Jeopardy (quiz yourself on converting between them; use "0.3..." for 0.3 with a bar (repeating decimal)) and/or Decention (finding equivalent fractions, decimals, and percentages).
And a Bonus From Previous Units.... Multiplication Facts and Factoring
Missing Multipliers (NRICH): I love these logic puzzles where you have to figure out what factors would give a mixed-up times table with the results inside, sort of Hangman-style. The challenges listed in links at the bottom of the page really are quite challenging!