The Jewish community of Cologne, Germany, designated the 23rd of Nissan as a day of fasting and mourning to commemorate the Jews of Cologne massacred in 1147 during the Second Crusade.
In remembrance of the tragic death of Rabbi Akiva's disciples who died in a plague in the weeks between Passover and Shavuot, several mourning practices are observed during this period: no marriages are conducted during this time, and like mourners, we don't cut our hair or enjoy the sound of music. Customs vary as to the proscribed activities and the dates during which the mourning is observed; consult your rabbi as to the traditions followed by your community.
Link: 24,000 Plus One
Tomorrow is the ninth day of the Omer Count. Since, on the Jewish calendar, the day begins at nightfall of the previous evening, we count the omer for tomorrow's date tonight, after nightfall: "Today is nine days, which are one week and two days, to the Omer." (If you miss the count tonight, you can count the omer all day tomorrow, but without the preceding blessing).
The 49-day "Counting of the Omer" retraces our ancestors' seven-week spiritual journey from the Exodus to Sinai. Each evening we recite a special blessing and count the days and weeks that have passed since the Omer; the 50th day is Shavuot, the festival celebrating the Giving of the Torah at Sinai.
Tonight's Sefirah: Gevurah sheb'Gevurah -- "Restraint in Restraint"
The teachings of Kabbalah explain that there are seven "Divine Attributes" -- Sefirot -- that G-d assumes through which to relate to our existence: Chessed, Gevurah, Tifferet, Netzach, Hod, Yesod and Malchut ("Love", "Strength", "Beauty", "Victory", "Splendor", "Foundation" and "Sovereignty"). In the human being, created in the "image of G-d," the seven sefirot are mirrored in the seven "emotional attributes" of the human soul: Kindness, Restraint, Harmony, Ambition, Humility, Connection and Receptiveness. Each of the seven attributes contain elements of all seven--i.e., "Kindness in Kindness", "Restraint in Kindness", "Harmony in Kindness", etc.--making for a total of forty-nine traits. The 49-day Omer Count is thus a 49-step process of self-refinement, with each day devoted to the "rectification" and perfection of one the forty-nine "sefirot."
Links:
How to count the Omer
The deeper significance of the Omer Count
The day following a festival is called Isru Chag ("tied to the festival"). Tachnun (confession of sins) and similar prayers are omitted.
Nothing is greater than peace. Even when you are 100% right, and you know your spouse is 100% wrong, you can still give in for the sake of peace.
Better a difficult peace than an easy quarrel.