Long-running free reference: Cyrillic alphabet, handwriting, grammar tables and tests.
Details
The alphabet section is the reason to bookmark it — how to pronounce, type and handwrite all 33 Cyrillic letters, which is the first two hours of anyone's Russian and often the worst-served. Beyond that there are grammar topics with tests, word-of-the-day lists and declension tables. Completely free and ad-supported; the design is firmly from an earlier internet era and some outbound links are stale.