Ashtanga- and Raja-Yoga 
At his time PATANJALI succeeded to bring a system into the Yoga in his Yoga-Sutras which completed the system of the early Samkhya to the Ishvara(Creator God).
But most of this Yoga was described before in the Sandilya - Upanishad of Atharvaveda.
This eightfolded path is in detail described in the Yoga Yajnavalkya, and it has been mentioned in further hinduist texts like the Linga Purana, the Devi Bhagavatam 7.35, the Sivasamhita and the Hathapradipika.
Eight steps
"Ashtanga Yoga--Yama, niyam, aasan, praanayaam, pratyaahaar, dhaarnaa, dhyaan, samaadhi, theses are the eight limbs of yoga. A Guru takes a disciple into these one by one."(Shankaraycharya Swaroopanand Saraswati, The Illustrated Weekly of India, September 13, 1987)
Patanjalis Yogasutras had nearly been forgotten since the 11th century and been revied in the last century. Chapter 2 (Sadhana pada) of the Yogasutras says : 27 : tasya saptadhā prānta-bhūmiḥ prajña (This path to enlightenment has 7 steps).
This system was often little understood, because Patanjali offered no special training-system with specific exercises except OM-Meditation, pranayama and asanas.
The 8 steps of Ashtanga - YOGA are equivalent to step 1 - 16 of the UNIVERSAL Path. Then follow three further samdhi-steps.
1. YAMA [ Tarot 1, 2 ] - Satya, Ahimsa, Brahmacharya, Aparigraha und Asteya
2. NIYAMA [ Tarot 3, 4 ] - Saucha, Santosha, Tapas, Swadhyaya and Ishwara Pranidhana
So the Ashtanga-Yoga has a kind of moral as its basis together with the study of the holy scriptures. Practices besides a change of lifestyle and of nutrition are the singing of special mantras.
The Hatha Yoga Pradipika mentions the above steps in 'Asanas 16,17'. and explains the Raja - Yoga.
3. ASANA : Body-exercises like in Hatha-Yoga, the beginnings of Tai Chi Chuan or the first steps of KungFu-Training [ Tarot 5, 6 ]
Yogasutra 2.47 : 'prayatna-śaithilyānanta-samāpattibhyām' : By relaxing effort and fixing the mind on the infinite [asana is perfected]. This step consists actually also of meditations on the infinite (as also the buddhist Culasuññata Sutta teaches).
4. PRANAYAMA - Purification of the life-force (Prana, Chi) [ Tarot 7, 8 ]
The chinese energy-exercises (Qi-Gong, Circulation of Chi) have a similar effect
5. PRATYAHARA - Drawing back of the senses [ Tarot 9, 10 ]
6. DHARANA - Concentration [ Tarot 11, 12 ]
7. DHYANA ( Meditation ) [ Tarot 13, 14 ]
The meditation is now so deep that it is the forrunner of Samadhi.
8. ISHVARA - SAMADHI (God - Extasy) [ Tarot 15, 16 ]
This is followed by further SAMADHIS like the Savikalpa Samadhi and the Nirvikalpa-Samadhi - the true Enlightenment with the Cosmic Consciousness, and finally the Sahaj-Samadhi of step 19 of the universal path.
Patanjali warns that the tempting Siddhis(occult forces) of very progressed yogis can be a hinderance that binds to the lower forces and planes.
27. The word of Ishvara, is OM. This is the Pranava.
28. Through the sounding of the Word and through reflection upon its meaning, the path is found.
Citations
"Engaged in the practice of concentration, uttering the monosyllable OM, remembering Me always, the yogi attains to the supreme goal." (Bhagavad Gita 8,13)
The Krama -Section of kashmir Shaivism practices a path similar to the Ashtanga - Yoga which requires first three double-stages.
“When you establish the internal reality of God Consciousness in Your soul, that is dharana. This dharana is not only to be established in internal God Consciousness but in all activities of the worldly life. This is true dharana." (Netra Tantra.)
* Three: " 1 for thou shalt have become that Three thyself. Thyself and mind, like twins upon a line, the star which is thy goal burns overhead. 2 The Three that dwell in glory and in bliss ineffable, now in the World of Maya have lost their names. They have become one star, the fire that burns but scorches not, that five which is the Upadhi3 of the Flame. And this, O Yogi of success, is what men call Dhyana, 4 the right percursor of Samadhi."(Blavatsky : Voice of Silence)
- Sivananda Raja-Yoga-Book Online
- A Wiki about Raja-Yoga
- The system of Samkhya as forerunner of Patanjali
- Raja - Yoga Sutras
- A comment to Yama and Niyama
- OM - Yoga - library
- Tibetan Monks : OM-Mantra
- The pranava yoga meditation