Anki
A good flashcard program will boost your ability to memorize vocabulary. These sometimes also go by the name Space Repetition System or SRS for short. Anki is by far the most popular.
Anki has a rich tool with a fairly steep learning curve. Many people start off with pre-made “shared decks” to bootstrap their language-learning. (These decks often go by the name Core2k, or something similar). Anki is highly recommended once you leave the beginner stage and start reading real material. It becomes a place where you can put words and phrases you look up so that you can remember them later.