There are a lot of questions here on Mi Yodeya about specific restrictions during the three weeks between 17 Tammuz and 9 Av, but I would like to know all of the things that are forbidden during the three weeks.
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Nitei Gavriel Bain HaMatzarim page 101 says that one may get engaged during the period of 17 Tamuz - 29 Tamuz, however no music or dancing is allowed.
Page 102 says that according to Ashkenazik custom we do not get married the entire 3 weeks, however Sefardic custom is to allow weddings during the period of 17 Tamuz - 29 Tamuz.
Page 116 says that one should not dedicate a new Sefer Torah the entire 3 weeks.
Page 119 says that since we do not make a Shehechiyanu on new clothing therefore one may purchase new clothing up to 29 Tamuz.
Page 125 says that one may say Shehechiyanu for a new daughter and for a Pidyon HaBen.
Page 126 One may move to a new apartment during these days, however it is best not to.
Page 129 says that no hair cutting is allowed the entire three weeks, however Sefardim only keep this during the week of Tisha B'Av.