Is it permitted to use Maaser money to sponsor a Kiddush in a Shul or to arrange a Farbrengen?
Yes, so long as one originally had the intention to use Maaser money when pledging to sponsor the Kiddush (or arrange the Farbrengen). Otherwise – i.e., if one already committed to do it without the intention of using Maaser money – it is not permitted.
The permission is granted provided the Kiddush/Farbrengen will assist in Torah and Mitzvos and the money spent on the food will be reasonable.
When using Maaser money, one should not make the Kiddush/Farbrengen in the Zechus of someone or something, unless some of the money is not from Maaser.
Additionally, one should not use Maaser money for a Kiddush/Farbrengen which is obligatory, such as in honor of one’s birthday etc.
.עיין רמ”א סימן רמט סעיף א וש”ך וט”ז שם ופ״ת ס״ק ב