Nitya Karma...

The word Nitya Karma means karma that recurs. It need not occur daily.
Of these things except the rituals concerning the manes others are done only by a few. We can see all those things and then discuss about the 40 samskaras.
Among the rituals concerning the manes most do the tharpana ritual on the new moon day . But there are 96 such dates on which the ritual is to be done. They are called shannavati tharpana.

Even the new moon day tharpana is in lieu of sradhdha. When the 96 tharpanas are rare what to say of 96th days of sradhdhda?
Any way let us list the ninety six days.
The first of the of the year – 1
(also known as yugadi)
The first day of Ayana. -2
(ayana are two; the northern sojourn of the sun is uththarayana, the southern sojourn of the sun is dhakshnayana.)
The First day of solar month - 12
The new moon days -12
manvathi -14
(These are days when the manvantharas started.)
First days of the four yugas. -4
(These are days when the yugas started mentioned as the lunar calendar days:
Vaikasi, shukla paksha 3rd day – krutha yuga started.
Karthika, shukla paksha ninth day – thretha yuga started.
Pathrapatha (Purattaasi) krisna paksha 13 th day dwapara yuga started.
Magha fullmoon day kali yuga started)

poorvedhyu, anvastaka, ashtaka – 12
(These are the eighth days of the waning moon, the days before and after that occurring in the hemantha and sisira ruthus.)
Mahalaya paksha – 15
Vytheepatha -12
Vaidhruthi -12
In addition to these two days in a year related to the parents. (the death anniversaries)
That makes it ninety six.

It is said that those who do the rituals on the yugadi and manvadi days satisfy the manes for 2000 years.

Some elders who know of things say that many of the problems that people face arise from the fact that the rituals concerning the manes is not done properly.

In these rituals there is a procedure that helps people who are barren. Not many people know of this.
Apart from these things are or what are called kamya sradhdhaa. These are done desiring something for which we are seeking the blessings of our ancestors.
The things desired can be swarga, progeny – boy or girl, ojas, lands, strength, something special, saubhagya, disease free life, growth of wealth etc.
These are listed by yagnavalkya. He also mentions the date, days and yoga etc. on which to do the rituals like these. Those who desire can search for it.
We are somehow slipped from daily rituals to rituals with desire.
In between there is something called naimithyakam. These arise in face of some special circumstances. For example if the hut of a agnihotri burns down a particular ishti is to be done.