Is there an app or web pages that makes clear fasting days for ROCOR? Especially Fish or Oil days? Is today 29 Jan a Fish allowable day?
I suggest saintjonah.org , which has rubrics for upcoming Holy Days. You can also buy a beautiful liturgical calendar from them that covers the entire year. By the way, the Triodion, which I think has information on fasting rules, is now downloadable from many sites.
In general, my experience has been the fasting rules are about the same between the North Slavic-derved denominations* like ROCOR, the MP, the OCA, the Church of Poland, the Church of Latvia, the Church of Lithuania, the Church of Belarus and the Church of Japan, except possibly the OCU and the UOCNA, which unfortunately has adopted several deviations from normal North Slavic practice implemented by the OCU (for example, switching from the Julian to the Revised Julian Calendar (previously, only some of the South Slavic churches such as the Bulgarians**, Czechs, Slovaks, and some OCA and Polish parishes used the Revised Julian Calendar)
*Excepting of course the Church of Finland and the EP portion of the Church of Estonia, whose canonical status is controversial, unlike the Church of Finland; these churches have adopted some Greek practices for example in the ranking of Metropolitans and Archbishops and in the use of the Gregorian Calendar and a somewhat toned down approach
** In terms of liturgical music and several other things, the Bulgarian Orthodox Church shares a great deal with the Russian, Ukrainian and Belarussian and other North Slavic heritage churches, whereas the Serbian Orthodox Church and the Church of the Czech Lands and Slovakia have their own distinct identities, the latter influenced by the Carpatho-Rusyn people who represent a substantial portion of the Orthodox population of those countries, along with ethnic Czechs and Slovaks of Orthodox persuasion. In the US, about half of the Bulgarian Orthodox parishes are part of the OCA and the other half are under the direct control of the Patriarch in Sofia.