Fard al Kifayah
Religious obligations in Islam which are obligatory are divided between farz ‘ayn , duties incumbent upon each individual and fard kifayah, those incumbent on the community as a whole.
Fard kafaayah means is that if it is not undertaken by enough people, then all the people are guilty of sin, but if enough people undertake it, the rest will be relieved of blame. Initially the command is addressed to all of them, as in the case of an individual obligation (fard ‘ayn), but then in the case of fard kafaayah the obligation is dropped if enough of the people undertake to do it, unlike the case with fard ‘ayn where the obligation is not dropped if someone else does it. 
1. Returning the greeting of salaam is obligatory if the greeting is given to one person. If it is given to a group, then it is obligatory upon the group (fard kifaayah or communal obligation; if one of the group returns the greeting, the obligation as been met). With regard to initiating the greeting, the basic principle is that it is Sunnah. It says in al-Mawsoo‘ah al-Fiqhiyyah (11/314):
Initiating the greeting is Sunnah mu’akkadah (a confirmed Sunnah) because the Prophet ﷺsaid: “Spread the greeting of salaam amongst yourselves.” It is obligatory to return the greeting if it is given to one person. If the greeting is given to a group, then in their case responding is a fard kifaayah (communal obligation); if one of them responds the sin is waived from the others, but if they all respond, they have all done what is required, Whether they respond all together or one after another. If they all refrain from responding, then they are all sinning because of the report which says: “The rights of one Muslim over another are five: returning (the greeting) of salaam…”
2. Visiting the sick it is a communal obligation. Shaykh Ibn ‘Uthaymeen said: Visiting the sick is a fard kifaayah (communal obligation). Majmoo‘ Fataawa wa Rasaa’il Ibn ‘Uthaymeen, 13/1085
3. Attending funerals is also a fard kifaayah (communal obligation)
4. Giving Advice to another Muslim.
5. Seeking knowledge regarding some knowledge is obligatory for ummah in general. If some of them do it in the required manner then the rest are absolved of responsibility, otherwise all of those who are able to do it are sinning. This is called fard kifaayah (communal obligation).Memorizing Qur’aan and hadeeth comes under the leading of the latter. The ummah is obliged to preserve the Book of Allaah and the hadeeth of His Messenger, whether in their hearts or on paper, so that nothing of the two sources of legislation will be lost.
6.Teaching the Qur’an is a communal obligation (fard kifaayah). If there is someone in the city who is teaching people the Qur’an, then there is no sin on a person, but he is missing out on a great deal of virtue.
7.Adhaan: The fuqaha’ are agreed that the adhaan is one of the unique features and manifest symbols of Islam, but they differ as to the rulings on it. Some say that it is fard kifaayah (a communal obligation); this is the view of Imam Ahmad and was the view favoured by Shaykh al-Islam Ibn Taymiyah; among contemporary scholars it is the view of Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him). And some said that it is Sunnah mu’akkadah. The correct view is that it is fard kifaayah; if someone who is competent does it, the rest are absolved of sin.
8. Da’wah: What appears to be the case based on the general meaning of the shar‘i evidence concerning that is that calling people to Allah, may He be exalted, is a communal obligation (fard kifaayah) upon the ummah and it is an individual obligation (fard ‘ayn) upon every Muslim, according to his level of ability and knowledge. The Prophet ﷺsaid: “Convey from me, even if it is only one verse.” Sahih al-Bukhari, 3461
The scholars have clearly stated that calling people to Allah, may He be exalted, is a communal obligation (fard kifaayah) with regard to the regions in which the callers live, for every region and area needs the da‘wah (call) and needs people who are active in this field. So it is a communal obligation; if sufficient numbers of people undertake it, the duty is waived from the others and for the others da‘wah becomes a confirmed Sunnah (Sunnah mu’akkadah) and a great righteous deed.
9.Moon Sighting: The majority of scholars are of the view that sighting the new moon of Ramadaan on the first night of the month is a communal obligation, and if all the people fail to do it then they are sinning.
10. Seeking knowledge which is beneficial for the Ummah as a whole like medicine, finance, engineering, etc is fard kifaayah.