  Brightness variations due to dark spots on the stellar surface encode
information about stellar surface rotation and magnetic activity. In this work,
we analyze the Kepler long-cadence data of 26,521 main-sequence stars of
spectral types M and K in order to measure their surface rotation and
photometric activity level. Rotation-period estimates are obtained by the
combination of a wavelet analysis and autocorrelation function of the light
curves. Reliable rotation estimates are determined by comparing the results
from the different rotation diagnostics and four data sets. We also measure the
photometric activity proxy Sph using the amplitude of the flux variations on an
appropriate timescale. We report rotation periods and photometric activity
proxies for about 60 per cent of the sample, including 4,431 targets for which
McQuillan et al. (2013a,2014) did not report a rotation period. For the common
targets with rotation estimates in this study and in McQuillan et al.
(2013a,2014), our rotation periods agree within 99 per cent. In this work, we
also identify potential polluters, such as misclassified red giants and
classical pulsator candidates. Within the parameter range we study, there is a
mild tendency for hotter stars to have shorter rotation periods. The
photometric activity proxy spans a wider range of values with increasing
effective temperature. The rotation period and photometric activity proxy are
also related, with Sph being larger for fast rotators. Similar to McQuillan et
al. (2013a,2014), we find a bimodal distribution of rotation periods.
