Mutawatir means successive. It is the highest form of sahih hadiths. Mutawatir hadiths have been narrated by so many hadith narrators that it is not conceivable that they have agreed upon a lie. Thus, mutawatir hadith is a form of hadith which is unquestionable.
There are only two types of texts in Islamic sharīʿah which are immutable (Qaati’). First, Verses of Quran and second, Mutawatir Hadith. If someone denies any verse of Quran or Mutawatir hadith, he does Kufr. Although scholars differed about exact number of mutawatir hadith.
Mutawatir hadith are of two types: Mutawatir in wording and meaning. Mutawatir in wording are those hadiths that have been narrated by many narrators with the same words. An example is the hadith: "Whoever intentionally attributes a lie against me, should prepare his seat in the Fire". This hadith had been narrated by atleast seventy-four companions of the Prophet Muhammad (PBUH), all with the same words. It is not conceivable that they agreed upon a lie about this hadith. So, it is a mutawatir hadith in wording.
Mutawatir in meaning are those hadiths where basic concept is the same. However, words or reported events may not be the same. For example: It is reported by a large number of narrators that Muhammad (PBUH) enjoined Muslims to perform two ra'kat in Fajr, four ra'kat in Dhuhr, Asr and Esha and three ra'kat in the Maghrib prayer. The words and reported events of this concept maybe different. But the common feature of all the reports is the same: the exact number of ra'kat. So, this is a mutawatir hadith in meaning.
Collection of Mutawatir hadith online in English is rare. Ministry of Islamic Affairs, Endowments, Da‘wah and Guidance, Kingdom of Saudi Arabia have a collection of mutawatir hadith. There are 324 hadiths. The link is here: Mutawatir Hadith Link.
These hadiths are compiled from the website by Nazmus Sakib Nirjhor, Nazim Uddin Rahi and Faroque Amin. It is published in slideshare.