Preterite tense:
conjuguemos.com/verb/138
conjuguemos.com/verb/137
www.spanishdict.com/quizzes/60/preterite-tense-forms
Double Object pronouns:
www.sporcle.com/games/SraLev/spanish-double-object-pronouns1
Future tense
conjuguemos.com/verb/116
reviewgamezone.com/game.php?id=41197
Comparatives
reviewgamezone.com/game.php?id=3448
www.purposegames.com/game/spanish-comparisons
Por vs Para
www.sporcle.com/games/TWH/spanish-por-vs-para----cause-and-effect
reviewgamezone.com/game.php?id=33272
www.spanish.cl/Grammar/Games/Por_Para.htm
www.quia.com/ba/74048.html?AP_rand=1490927566
www.spanishnewyork.com/automatic/porpara.php
Present Subjuntive
beta.conjuguemos.com/verb/frog_game/129
beta.conjuguemos.com/verb/battleship/129
reviewgamezone.com/games4/snow.php?test_id=30657&title=Regular%20Present%20Subjunctive
reviewgamezone.com/games4/ants.php?test_id=30657&title=Regular%20Present%20Subjunctive
reviewgamezone.com/games4/paperbird.php?test_id=30657&title=Regular%20Present%20Subjunctive
reviewgamezone.com/games4/taxi.php?test_id=30657&title=Regular%20Present%20Subjunctive
reviewgamezone.com/games4/free-kick.php?test_id=30657&title=Regular%20Present%20Subjunctive
Negative tu commands
www.quia.com/rr/1195645.html
www.purposegames.com/game/negative-tu-commands-game
www.quia.com/ba/258840.html
www.123teachme.com/games/tank/category/command_tu_negative
Destinos:
learner.org/series/destinos/
www.purposegames.com/game/spanish-know-your-preterite-vsimperfect
Useful links:
www.bowdoin.edu/~eyepes/newgr/ats/