Nowadays sufism can very much be compared to kabbala. Kabbala is to my knowledge a part of Judaism in its more spiritual/mystical sense. And has been practiced by Jews for ages now. Sufism has always been accepted as part of Sunni Islam and is about getting closer to God as His servant, deepening our servitude to Him and increasing the spiritual fruits of it. Whereas other sciences of Islam are about the outer parts of Islam such as legalistic or theological questions/deepening.
Jalalluddin Rumi had studied Islamic law/jurisprudence, adhered to it but sought a deeper personal meaning. That's when he met his (spiritual) master Shams and traveled his journey to a deeper understanding of Islam and getting closer to God. That inner path is called sufism. And he left a beautiful book of poetry full of wisdom: The Mathnawi. To achieve this state there are practices of course, packed in a certain "philosophy" and focused on ourselves, character, spiritual diseases of our heart in order to come closer to God.
But nowadays sufism, as well as kabbala in Judaism, developed outside the realm of Islam as well. Just as Kabbala is also existent as a universal theory outside Judaism and teached as such. This does not mean sufism within an Islamic framework does not exist anymore. It has been alive and still is very much alive actually. Countries such as Pakistan/India, Sudan, Morocco, Turkey, Chechnya, Indonesie, Jemen and Senegal have an Islamic culture that is strongly influenced by sufi's and sufism. One who knows can see their traces everywhere, in practices, at graves, poetry,important historical figures etc etc.
It just means that nowadays two kinds of "sufisms" are practiced: the old, traditional, sufism as a part of Islam and within Islamic creed. And a universal-orientalistic one not limited to Islamic creed. An example of the universal sufis is the Treshhold society in North America. An example of traditional Muslim sufi's is the Naqshbandi-Haqani sufi circle in North America & Europe. Following Sheikh Nazim, living in North-Cyprus (Lefke).